Publication Search Results

ID: 152259
Type: article
Authors: Acosta-Rangel, Aleyda; Li, Rui; Celis, Nydia; Suárez, Donald L.; Santiago, Louis S.; Arpaia, Mary Lu; Mauk, Peggy A.
Keywords: STRI
Abstract: With increasing demands on both potable and agricultural water supplies, drought, and extreme temperatures worldwide, agricultural production is challenged with reduced water availability and lower water quality. Salinity, which is associated with low water quality is a critical issue for California avocado growers and, coupled with avocado root rot, threatens the long-term sustainability of the industry since avocados (Persea americana Mill.) are known to be extremely salt sensitive. Salt tolerance of the ‘Hass’ variety, the most commonly grown scion in California, is influenced by rootstock. We investigated ‘Hass’ scions grafted onto three different avocado rootstocks under control (irrigation using water with EC = 0.65 dS/m) and salinity (irrigation using water with EC = 1.5 dS/m) conditions. Results indicated that, compared to control conditions, the irrigation of avocado trees using water with EC = 1.5 dS/m increased canopy damage by 44%, reduced survival by half of the trees tested, and caused yield losses of more than 63%. Avocado leaves visibly damaged by the salinity treatment (named as partially burned or PB leaves) experienced photoinhibition, and reduction of photosynthetic rate and water-use efficiency, suggesting that the poor performance in carbon assimilation contributed to reductions in yield and increases in mortality. The salinity treatment did not cause water stress and the poor performance of treated trees was attributable to chloride accumulation previously reported. Leaf carbon isotopic composition was affected in trees under salinity treatment by increasing the values of δ13C however, this affect was nor correlated with water-use efficiency. Overall, ‘R0.05’, ‘PP40’ and ‘Dusa’ performed similarly and, considering the conditions of the experiment and the intrinsic susceptibility of avocado trees to salinity, were superior to all other rootstocks tested. Future screenings for salinity tolerant rootstocks are required to improve yield when poor quality soil or water is used. Overall, our results showed a coordination between the physiological performance, health and productivity of the ‘Hass’ scion and how these parameters were negatively affected by salinity.

ID: 150713
Type: article
Authors: Adamowicz, Wiktor; Calderon-Etter, Laura; Entem, Alicia; Fenichel, Eli P.; Hall, Jefferson S.; Lloyd-Smith, Patrick; Ogden, Fred L.; Regina, Jason A.; Rad, Mani Rouhi; Stallard, Robert F.
Keywords: STRI
Abstract: Conventional markets can underprovide ecosystem services. Deliberate creation of a market for ecosystem services e.g., a payments for ecosystem services (PES) scheme] can close the gap. The new ecosystem service market alters behaviors and quantities of ecosystem service provided and reveals prices for the ecosystems service: a market-clearing equilibrium. Assessing the potential for PES programs, which often act as ecological infrastructure investment mechanisms, requires forecasting the market-clearing equilibrium. Forecasting the equilibrium is complicated, especially at relevant social and ecological scales. It requires greater disciplinary integration than valuing ecosystem services or computing the marginal cost of making a land-use change to produce a service. We conduct an ex ante benefit–cost assessment and forecast market-clearing prices and quantities for ecological infrastructure investment contracts in the Panama Canal Watershed. The Panama Canal Authority could offer contracts to private farmers to change land use to increase dry-season water flow and reduce sedimentation. A feasible voluntary contracting system yields a small program of about 1,840 ha of land conversion in a 279,000-ha watershed and generates a 4.9 benefit–cost ratio. Physical and social constraints limit market supply and scalability. Service delays, caused by lags between the time payments must be made and the time services stemming from ecosystem change are realized, hinder program feasibility. Targeting opportunities raise the benefit–cost ratio but reduce the hectares likely to be converted. We compare and contrast our results with prior state-of-the-art assessments on this system.

ID: 152689
Type: article
Authors: Adams, Benjamin J.; Gora, Evan M.; Breugel, Michiel van; Estrada-Villegas, Sergio; Schnitzer, Stefan A.; Hall, Jefferson S.; Yanoviak, Stephen P.
Keywords: STRI
Abstract: Almost half of lowland tropical forests are at various stages of regeneration following deforestation or fragmentation. Changes in tree communities along successional gradients have predictable bottom-up effects on consumers. Liana (woody vine) assemblages also change with succession, but their effects on animal succession remain unexplored. Here we used a large-scale liana removal experiment across a forest successional chronosequence (7–31 years) to determine the importance of lianas to ant community structure. We conducted 1,088 surveys of ants foraging on and living in trees using tree trunk baiting and hand-collecting techniques at 34 paired forest plots, half of which had all lianas removed. Ant species composition, β-diversity, and species richness were not affected by liana removal; however, ant species co-occurrence (the coexistence of two or more species in a single tree) was more frequent in control plots, where lianas were present, versus removal plots. Forest stand age had a larger effect on ant community structure than the presence of lianas. Mean ant species richness in a forest plot increased by ca. 10% with increasing forest age across the 31-year chronosequence. Ant surveys from forest >20 years old included more canopy specialists and fewer ground-nesting ant species versus those from forests <20 years old. Consequently, lianas had a minimal effect on arboreal ant communities in this early successional forest, where rapidly changing tree community structure was more important to ant species richness and composition.

ID: 151812
Type: article
Authors: Adams, Benjamin J.; Schnitzer, Stefan A.; Yanoviak, Stephen P.
Keywords: STRI
Abstract: Understanding how habitat structure and resource availability affect local species distributions is a key goal of community ecology. Where habitats occur as a mosaic, variation in connectivity among patches influences both local species richness and composition, and connectivity is a key conservation concern in fragmented landscapes. Similarly, availability of limiting resources frequently determines species co-existence or exclusion. For primarily cursorial arthropods like ants, gaps between neighboring trees are a significant barrier to movement through the forest canopy. Competition for limited resources such as nest sites also promotes antagonistic interactions. Lianas (woody vines) connect normally isolated neighboring tree crowns and often have hollow stems inhabited by ants. We used two large-scale liana removal experiments to determine how connectivity and nest site availability provided by lianas affect arboreal ant species richness, species composition, and β-diversity in a lowland tropical forest in Panama. Removing lianas from a tree crown reduced ant species richness up to 35%, and disproportionately affected species that require large foraging areas. Adding artificial connectivity to trees mitigated the effects of liana removal. Ant colonization of artificial nests was higher (73% occupied) in trees without lianas vs. trees with lianas (28% occupied). However, artificial nests typically were colonized by existing polydomous, resident ant species. As a result, nest addition did not affect ant community structure. Collectively, these results indicate that lianas are important to the maintenance of arboreal ant diversity specifically by providing connectivity among neighboring tree crowns. Anticipated increases in liana abundance in this forest could increase the local (tree-level) species richness of arboreal ants, with a compositional bias toward elevating the density of broad-ranging specialist predators. This article is protected by copyright. All rights reserved.

ID: 151538
Type: article
Authors: Aguilar-Rodríguez, Pedro Adrián; Tschapka, Marco; García-Franco, José G.; Krömer, Thorsten; MacSwiney G, ,M.Cristina
Keywords: STRI
Abstract: Pollinators can be a limited resource and natural selection should favour differences in phenotypic characteristics to reduce competition among plants. Bats are important pollinators of many Neotropical plants, including the Bromeliaceae; however, the pre-pollination mechanisms for isolation among sympatric bat-pollinated bromeliads are unknown. Here, we studied the mechanisms for reproductive segregation between Pitcairnia recurvata, Pseudalcantarea viridiflora, Werauhia noctiflorens and W. nutans. The study was conducted at Los Tuxtlas Biosphere Reserve, in Veracruz, Mexico We carried out ex situ and in situ manual pollination treatments to determine the breeding system by assessing fruiting and seedling success and sampled bat visitors using mist-nets and infrared cameras. We determined the nocturnal nectar production pattern, estimating the energetic content of this reward. All four bromeliads are self-compatible, but only P. recurvata appears to require pollinators, because the physical separation between anthers and stigma prevents self-pollination, it is xenogamous and presents a strictly nocturnal anthesis. The bats Anoura geoffroyi, Glossophaga soricina and Hylonycteris underwoodi are probable pollinators of three of the studied bromeliads. We did not record any animal visiting the fourth species. The flowering season of each species is staggered throughout the year, with minimal overlap, and the floral morphology segregates the locations on the body of the bat where the pollen is deposited. The most abundant nectar per flower is provided by P. viridiflora, but P. recurvata offers the best reward per hectare, considering the density of flowering plants. Staggered flowering, different pollen deposition sites on the body of the pollinator and differences in the reward offered may have evolved to reduce the competitive costs of sharing pollinators while providing a constant supply of food to maintain a stable nectarivorous bat community.

ID: 151543
Type: article
Authors: Almeida, Danilo R. A.; Stark, Scott C.; Schietti, Juliana; Camargo, Jose L. C.; Amazonas, NinoT; Gorgens, Eric B.; Rosa, Diogo M.; Smith, Marielle N.; Valbuena, Ruben; Saleska, Scott; Andrade, Ana; Mesquita, Rita; Laurance, Susan G.; Laurance, William F.; Lovejoy, Thomas E.; Broadbent, Eben N.; Shimabukuro, Yosio E.; Parker, Geoffrey G.; Lefsky, Michael; Silva, Carlos A.; Brancalion, Pedro H. S.
Keywords: STRI; SERC
Abstract: Assessing the persistent impacts of fragmentation on above ground structure of tropical forests is essential to understanding the consequences of land use change for carbon storage and other ecosystem functions. We investigated the influence of edge distance and fragment size on canopy structure, aboveground woody biomass (AGB), and AGB turnover in the Biological Dynamics of Forest Fragments Project (BDFFP) in central Amazon, Brazil, after 22+ years of fragment isolation, by combining canopy variables collected with Portable Canopy profiling lidar and airborne laser scanning surveys with long-term forest inventories. Forest height decreased by 30% at edges of large fragments (> 10 ha) and interiors of small fragments (< 3 ha). In larger fragments, canopy height was reduced up to 40 m from edges. Leaf area density profiles differed near edges: the density of understory vegetation was higher and midstory vegetation lower, consistent with canopy reorganization via increased regeneration of pioneers following post-fragmentation mortality of large trees. However, canopy openness and leaf area index remained similar to control plots throughout fragments, while canopy spatial heterogeneity was generally lower at edges. AGB stocks and fluxes were positively related to canopy height and negatively related to spatial heterogeneity. Other forest structure variables typically used to assess the ecological impacts of fragmentation (basal area, density of individuals, and density of pioneer trees) were also related to lidar-derived canopy surface variables. Canopy reorganization through the replacement of edge-sensitive species by disturbance-tolerant ones may have mitigated the biomass loss effects due to fragmentation observed in the earlier years of BDFFP. Lidar technology offered novel insights and observational scales for analysis of the ecological impacts of fragmentation on forest structure and function, specifically aboveground biomass storage. This article is protected by copyright. All rights reserved.

ID: 152250
Type: article
Authors: Amador-Vargas, Sabrina
Keywords: STRI
Abstract: Mutualistic species often associate with several partners that vary in the benefits provided. In some protective ant–plant mutualisms, ants vary in the extent at which they kill neighboring vegetation. Particularly, in acacia ants (Pseudomyrmex), the area around the host tree that ants keep free from vegetation (“clearings”) vary depending on the species. This study assessed whether interspecific variation in clearing size corresponds to workers biting on plant tissue of different thickness. As expected, workers from species making the largest clearings bit more often on thicker plant tissues than workers from species making smaller clearings. Because head shape affects mandible force, I also assessed whether pruning on thick tissue in mutualistic ant species or being a predator in non-mutualistic species correlated with broader heads, which yield stronger mandible force. The species with the broader heads were non-mutualistic predators or mutualistic pruners of thick tissues, which suggest that pruning neighboring vegetation in non-predatory species demands force even when the ants do not kill prey with their mandibles. The findings reveal that clearing size variation in mutualistic ant partners of plants can also be observed at the level of individual decision-making processes among workers, and suggest that head morphology could be a trait under selection in protective ant–plant mutualisms. Abstract in Spanish is available with online material.

ID: 150608
Type: article
Authors: Aninta, Sabhrina G.; Rocha, Ricardo; López-Baucells, Adrià; Meyer, Christoph F. J.
Keywords: STRI
Abstract: The traditional focus on taxonomic diversity metrics for investigating species responses to habitat loss and fragmentation has limited our understanding on how biodiversity is impacted by habitat modification. This is particularly true for taxonomic groups such as bats which exhibit species-specific responses. Here, we investigate phylogenetic alpha and beta diversity of Neotropical bat assemblages across two environmental gradients, one in habitat quality and one in habitat amount. We surveyed bats in 39 sites located across a whole-ecosystem fragmentation experiment in the Brazilian Amazon, representing a gradient of habitat quality (interior-edge-matrix, hereafter IEM) in both continuous forest and forest fragments of different sizes (1, 10, and 100 ha; forest size gradient). For each habitat category, we quantified alpha and beta phylogenetic diversity, then used linear models and cluster analysis to explore how forest area and IEM gradient affect phylogenetic diversity. We found that the secondary forest matrix harboured significantly lower total evolutionary history compared to the fragment interiors, especially the 1 ha fragments, containing bat assemblages with more closely related species. Forest fragments ≥10 ha had levels of phylogenetic richness similar to continuous forest, suggesting that large fragments retain considerable levels of evolutionary history. The edge and matrix adjacent to large fragments tend to have closely related lineages nonetheless, suggesting phylogenetic homogenization in these IEM gradient categories. Thus, despite the high mobility of bats, fragmentation still induces considerable levels of erosion of phylogenetic diversity, suggesting that the various evolutionary history might not be able to persist in present-day human-modified landscapes.

ID: 152174
Type: article
Authors: Anker, Arthur
Keywords: STRI
Abstract: The present study deals with five species of the alpheid shrimp genus Salmoneus Holthuis, 1955 from the tropical eastern Pacific. One of them is new to science and is described as Salmoneus tiburon sp. nov. The new species is presently known only from the Las Perlas Archipelago in Panama and can be distinguished from all other congeners by the dentition on the cutting edges of the major chela, with some dactylar teeth reminiscent of shark teeth. It is also one of the largest species of the genus, with the carapace length of both type specimens surpassing 8.0 mm. Salmoneus serratidigitus (Coutière, 1897), a species with an ample distribution across the Indo-Pacific, is recorded for the first time from the Pacific coast of Panama and is confirmed from Colombia. Salmoneus malagensis Anker & Lazarus, 2015, previously known only from Bahía Málaga in Colombia, is recorded from Panama’s Azuero Peninsula. The remaining two species, S. excavatus Anker, 2011 and S. alvarezi Anker & Lazarus, 2015, are recorded regionally from Las Perlas Archipelago in Panama and Playa Tarcoles in Costa Rica, both for the first time since their original descriptions. An identification key to the five currently known eastern Pacific species of Salmoneus is provided. However, several immature and/or incomplete specimens herein preliminarily reported as Salmoneus spp., as well photographic records from southern California, USA, indicate the presence of further undescribed species in the eastern Pacific.

ID: 152188
Type: article
Authors: Anker, Arthur; Pachelle, Paulo P. G.
Keywords: STRI
Abstract: A new snapping shrimp, Alpheus perlas sp. nov., is described based on a single complete male specimen collected on a shallow mudflat at Casayeta Island in the Las Perlas Archipelago, Gulf of Panama. The new species belongs to the large A. edwardsii (Audouin, 1821) species group characterised essentially by the presence of two notches on the major chela palm, with the dorsal notch extending posteriorly on the mesial surface. Within the eastern Pacific members of the A. edwardsii group, A. perlas sp. nov. appears to be morphologically closest to A. latus Kim & Abele, 1988 and A. burukovskyi Anker & Pachelle, 2015. Alpheus perlas sp. nov. does not seem to be specially adapted for digging and may be inquiline of a larger burrowing host, which currently remains unknown.

ID: 152177
Type: article
Authors: Arellano, Gabriel
Keywords: STRI
Abstract: Many ecological applications, like the study of mortality rates, require the estimation of proportions and confidence intervals for them. The traditional way of doing this applies the binomial distribution, which describes the outcome of a series of Bernoulli trials. This distribution assumes that observations are independent and the probability of success is the same for all the individual observations. Both assumptions are obviously false in many cases. I show how to apply bootstrap and the Poisson binomial distribution (a generalization of the binomial distribution) to the estimation of proportions. Any information at the individual level would result in better (narrower) confidence intervals around the estimation of proportions. As a case study, I applied this method to the calculation of mortality rates in a forest plot of tropical trees in Lambir Hills National Park, Malaysia. I calculated central estimates and 95% confidence intervals for species-level mortality rates for 1,007 tree species. I used a very simple model of spatial dependence in survival to estimate individual-level risk of mortality. The results obtained by accounting for heterogeneity in individual-level risk of mortality were comparable to those obtained with the binomial distribution in terms of central estimates, but the precision increased in virtually all cases, with an average reduction in the width of the confidence interval of 20%. Spatial information allows the estimation of individual-level probabilities of survival, and this increases the precision in the estimates of mortality rates. The general method described here, with modifications, could be applied to reduce uncertainty in the estimation of proportions related to any spatially structured phenomenon with two possible outcomes. More sophisticated approaches can yield better estimates of individual-level mortality and thus narrower confidence intervals.

ID: 148506
Type: article
Authors: Arellano, Gabriel; Medina, Nagore G.; Tan, Sylvester; Mohamad, Mohizah; Davies, Stuart J.
Keywords: STRI
Abstract: What causes individual tree death in tropical forests remains a major gap in our understanding of the biology of tropical trees and leads to significant uncertainty in predicting global carbon cycle dynamics. We measured individual characteristics (diameter at breast height, wood density, growth rate, crown illumination and crown form) and environmental conditions (soil fertility and habitat suitability) for 26 425 trees ≥ 10 cm diameter at breast height belonging to 416 species in a 52-ha plot in Lambir Hills National Park, Malaysia. We used structural equation models to investigate the relationships among the different factors and tree mortality. Crown form (a proxy for mechanical damage and other stresses) and prior growth were the two most important factors related to mortality. The effect of all variables on mortality (except habitat suitability) was substantially greater than expected by chance. Tree death is the result of interactions between factors, including direct and indirect effects. Crown form/damage and prior growth mediated most of the effect of tree size, wood density, fertility and habitat suitability on mortality. Large-scale assessment of crown form or status may result in improved prediction of individual tree death at the landscape scale.

ID: 153443
Type: article
Authors: Arellano-Torres, Elsa; Correa-Metrio, Alexander; López-Dávila, Diego; Escobar, Jaime; Curtis, Jason H.; Cordero-Oviedo, Mar
Keywords: STRI
Abstract: We studied a 13-meter sediment core collected from La Mancha coastal lagoon, Veracruz, Mexico, to determine paleoenvironmental variations linked to the mid- to late Holocene sea-level rise. We examined modern and fossil benthic foraminiferal assemblages, isotopic values in tests of Ammonia tepida (δ18O-foram and δ13C-foram), δ13C in organic matter (δ13C-org), and sediment elemental ratios (Fe/Ca, Ca/Ti, and K/Rb) to reconstruct salinity variations, coastal processes, and the morphologic evolution of a partially closed coastal lagoon. We identified four main periods of environmental change: (1) From ~7800 to 6500 cal. yr. BP, the core site was an open lagoon with higher oceanic influence than today, through the presence of a southern mouth, as evidenced by the euryhaline assemblage Ammonia-Quinqueloculina-Bolivina-Nonionella. Low δ18O-foram and high δ13C values on foraminifera shells indicate greater inputs of seawater, and δ13C-org values reflect a lagoon environment. Elemental ratios of lower Fe/Ca, moderate Ca/Ti, and higher K/Rb suggest increased coastal weathering and reduced detrital deposits than today. (2) From ~6500 to 4600 cal. yr. BP., the lagoon experienced the progressive closure of the southern mouth, to the point that sedimentation restricted seawater entrance, as evidenced by variable δ13C-org values, a lowering trend in δ18O-foram and δ13C-foram values, low Fe/Ca, higher Ca/Ti but moderate K/Rb values. At this time, benthic foraminifera were dominated by the opportunistic Ammonia-Elphidium polyhaline assemblage. (3) From ~4600 to 1400 cal. yr. BP, the northern mouth was the only source of seawater to the lagoon, establishing the optimal environment for calcareous foraminifera of the polyhaline assemblage Ammonia-Elphidium. Lowest δ13C-org values indicate greater organic input by terrestrial plants. (4) At 1400 cal. yr. BP, modern conditions of a partially closed lagoon were established, while increased terrigenous inputs and freshwater runoff favored the growth of agglutinated foraminifera species. At millennial time scales, in addition to the sea level rise effects, the lagoon evolution fits in the paleoclimatic context that links insolation, the latitudinal change of ITCZ, ocean currents, longshore drift and moisture transport, as driving factors of morphological change in the western coast of the Gulf of Mexico.

ID: 153445
Type: article
Authors: Assemat, Alexandre; Boivin, Myriam; Marivaux, Laurent; Pujos, François; Benites-Palomino, Aldo; Salas-Gismondi, Rodolfo; Tejada-Lara, Julia; Varas-Malca, Rafael; Negri, Francisco Ricardo; Ribeiro, Ana Maria; Antoine, Pierre-Olivier
Keywords: STRI

ID: 153430
Type: article
Authors: Baldwin, Justin W.; Dechmann, Dina K. N.; Thies, Wibke; Whitehead, Susan R.
Keywords: STRI
Abstract: The paradoxical presence of toxic chemical compounds in ripe fruits represents a balance between plant enemies and allies: chemical traits can defend seeds against antagonistic herbivores, seed predators or fungal pathogens, but also can impose costs by repelling mutualistic seed dispersers, although the costs are often difficult to quantify. Seeds gain fitness benefits from travelling far from the parent plant, as they can escape from parental competition and elude specialized herbivores as well as pathogens that accumulate on adult plants. However, seeds are difficult to follow from their parent plant to their final destination. Thus, little is known about the factors that determine seed dispersal distance. We investigated this potential cost of fruit secondary compounds – reduced seed dispersal distance - by combining two datasets from previous work on a Neotropical bat-plant dispersal system (bats in the genus Carollia and plants in the genus Piper). We used data from captive behavioral experiments, which show how amides in ripe fruits of Piper decrease the retention time of seeds and alter food choices. With new analyses, we show that these defensive secondary compounds also delay the time of fruit removal. Next, with a behaviorally annotated bat telemetry dataset, we quantified post-feeding movements (i.e. seed dispersal distances). Using generalized additive mixed models we found that seed dispersal distances varied nonlinearly with gut retention times as well as with the time of fruit removal. By interrogating the model predictions, we identified two novel mechanisms by which fruit secondary compounds can impose costs in terms of decreased seed dispersal distances: 1) small scale reductions in gut retention time and 2) causing fruits to forgo advantageous bat activity peaks that confer high seed dispersal distances.

ID: 151915
Type: article
Authors: Baranov, Viktor; Kvifte, Gunnar M.; Müller, Patrick; Bernal, Ximena E.
Keywords: STRI
Abstract: Frog-biting midges (Diptera: Corethrellidae) are hematophagous flies in which females feed on anuran blood using the mating calls produced by calling male frogs. This family is of large ecological, evolutionary and ethological interest, but its geological history is poorly known. We describe a new species of frog-biting midge (Diptera, Corethrellidae), Corethrella patula sp. nov., from mid-Cretaceous Burmese amber (ca. 99 Ma). This new species is distinct from Corethrella andersoni, known from the same deposit, differing in having more slender mid femora and a triangular bifid tarsal segment 5 without scales. These two species, however, share an apparent synapomorphy in the wing; R2 vein diverting from R2+3 at 75° angle in relation to R3. The well-preserved male genitalia of the new species suggest C. patula and C. andersoni are a distinct, early lineage not easily placeable within either of the described subgenera of Corethrella.

ID: 151807
Type: article
Authors: Bashevkin, Samuel M.; Christy, John H.; Morgan, Steven G.
Keywords: STRI
Abstract: Plankton live under the countervailing selective pressures of predation and ultraviolet radiation (UVR). In lakes, zooplankton are transparent reducing visibility to predatory fishes but are pigmented in the absence of fishes, hypothetically reducing UVR damage. In the sea, planktivorous fishes are widespread, so plankton typically are transparent and ascend to productive surface waters at night to forage and descend during the day to reduce visibility to predators. However, larvae of some species face the unique constraint of traveling in surface currents in the daytime during migrations between adult and larval habitats. We would expect these larvae to be transparent since companion studies demonstrated increased predation risk of pigmented larvae under strong sunlight. Paradoxically, larvae range from being darkly to lightly pigmented. We hypothesize that some larvae are more heavily pigmented to reduce UVR damage, while other species travelling in subsurface currents with low UVR might be more transparent. Linking larval morphology to depth-dependent selective pressures would add a key element to help improve predictions of larval vertical distributions, which are important for simulating larval transport trajectories. We quantitatively tested the hypothesis that selection may have favored photoprotective pigmentation for larvae in the predominantly transparent plankton community while testing the differential effects of UVA and UVB radiation. We measured larval pigmentation of 12 species of crabs and exposed them to visible light only, visible + UVA, or visible + UVA + UVB in the tropics. Controlling for phylogeny, more pigmented species survived UVR better than less pigmented species, especially on sunnier days, though intraspecific comparisons for four species were equivocal. Most species died even from UVA exposure, which has long been regarded as relatively harmless despite penetrating deeper underwater than UVB. Thus, we demonstrate with a phylogenetically controlled analysis that crab larvae are pigmented in the predominantly transparent planktonic community to protect from UVR, improving our understanding of the selective forces acting on animal coloration and the factors determining planktonic distributions, survival, and dispersal. This linkage of morphology with susceptibility will be important for developing mechanistic models of environmental stress responses to better predict larval dispersal in current and future climates. This article is protected by copyright. All rights reserved.

ID: 152691
Type: article
Authors: Bashevkin, Samuel M.; Christy, John H.; Morgan, Steven G.
Keywords: STRI
Abstract: Morphological defenses of plankton can include armor, spines, and coloration. Spines defend from gape-limited fish predators while pigmentation increases visibility to fishes but defends from ultraviolet radiation (UVR). Planktonic crab larvae (zoeae) exhibit inter- and intra-specific variability in the lengths of defensive spines, extent of pigmentation, and body size. The determinants of this variability and the relationships among these traits are largely unknown. Larvae may employ generalized defenses against the dual threats of UVR and predation or specialized defenses against their primary threat, with an unknown role of allometric or phylogenetic constraints. Generalization would result in longer spines compensating for the increased predation risk imposed by darker pigments, while specialization would lead to more investment in either defense from predation (long spines) or UVR (dark pigments), at the expense of the other trait. We examined 1) the relationship between spine lengths and pigmentation, 2) the scaling of spine lengths with body size, and 3) phylogenetic constraint in spine lengths, pigmentation, and body size, among and within 21 species of laboratory-hatched and 23 species of field-collected crab larvae from Panama and California. We found a negative relationship between spine length and pigmentation among species from laboratory and field. Within species, we found a marginally significant negative relationship among field-collected larvae. Spine lengths showed positive allometric scaling with carapace length while spine and carapace lengths, but not pigmentation, had significant phylogenetic signals. The negative relationship we observed between pigmentation and spine length supports our defense specialization hypothesis. Positive allometric scaling of spine lengths means larger larvae are better defended from predators, which may indicate that larvae face greater predation risk as they grow larger. Phylogenetic constraint may have arisen because related species encounter similar predation threats. Conversely, phylogenetic constraint in the evolution of spine lengths may induce convergent behaviors resulting in related species facing similar predation threats. Our results improve understanding of the evolution of the larval morphology of crabs, morphological defenses in the plankton, and evolutionary responses of morphology to multiple spatially-segregated selective forces.