If larvae were smart: a simple model for optimal settlement behavior of competent larvae

Much research has been done on larval settlement cues. Rather than having simple fixed responses to constant environmental stimuli, it seems likely that settlement decisions made by individual larvae should vary depending on the individual and the conditions under which it encounters that cue. Here, we present a simple stochastic dynamic programming model that explores the conditions under which larvae may maximize their lifetime fitness by accepting lower quality habitat rather than continuing to search for superior habitat. Our model predicts that there is a relatively narrow range of parameter values over which larval selectivity among habitat types changes dramatically from 1 (larvae accept only optimal substrata) to 0 (indiscriminant settlement). This narrow range coincides with our best estimate of parameter values gleaned from empirical studies, and the model output matches data for the polychaete worm Hydroides dianthus remarkably well. The relative availability of habitats and the total time available to search for high quality habitat (i.e. the ability to delay metamorphosis) had the greatest effects on larval selectivity. In contrast, intuitive factors, including larval energetics and mortality, showed little effect on larval habitat preference, but could still alter the proportion of larvae settling in different habitats by reducing search time. Our model predicts that a given larva may behave differently depending on where it falls in the optimality decision matrix at the instant in which it locates substrata. This model provides a conceptual framework in which to conduct future studies involving variability in settlement decisions among individual larvae, and in which to consider the selective forces driving the evolution of specific larval settlement cues. Our results suggest that a combination of the maximum search period and the relative frequency and quality of optimal habitat likely exert the greatest influence on the evolution of larval selectivity in the field

Is post-bleaching recovery of Acropora hyacinthus on Palau via spread of local kin groups?

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cros, A., Toonen, R., & Karl, S. A. Is post-bleaching recovery of Acropora hyacinthus on Palau via spread of local kin groups? Coral Reefs, (2020), doi:10.1007/s00338-020-01961-3.Palau suffered massive mortality of reef corals during the 1998 mass bleaching, and understanding recovery from that catastrophic loss is critical to management for future impacts. Many reef species have shown significant genetic structure at small scales while apparently absent at large scales, a pattern often referred to as chaotic genetic patchiness. Here we use hierarchical sampling of population structure scored from a panel of microsatellite markers for the coral Acropora hyacinthus across the islands of Yap, Ngulu and Palau to evaluate hypotheses about the mechanisms of previously described chaotic genetic structure. As with previous studies, we find no isolation-by-distance within or between the three islands and high genetic structure between sites separated by as little as ~ 10 km on Palau. Using kinship among individual colonies, however, we find higher mean pairwise relatedness coefficients among individuals within sampling sites. Comparing population structure among hierarchical sampling scales, we show that the pattern of chaotic genetic patchiness reported previously appears to derive from genetic patches of local kin groups at small spatial scales. Genetic distinction of Palau from neighboring islands and high kinship among individuals within these kinship neighborhoods implies that the coral reefs of Palau apparently recovered through a mosaic of rare thermally tolerant colonies that survived the 1998 mass bleaching and are now spreading and recolonizing reefs as local kin groups. This pattern of recovery on Palau gives us a better understanding for effective coral reef conservation strategies in which protecting these rare survivors wherever they occur, rather than specific areas of reef habitat, is critical to increase coral reef resilience.This work was supported by the Disney Wildlife Conservation Fund to A Cros and SA Karl; the Graduate Women in Science Adel Lewis Grant Fellowship; the Founder Region Fellowship; the Ecology Evolution Conservation Biology Watson T. Yoshimoto grant and the Colonel Willys E. Lord Scholarship Award to A Cros; and a National Science Foundation grant OCE 14-16889 to RJ Toonen

Rare coral under the genomic microscope: timing and relationships among Hawaiian Montipora

Background Evolutionary patterns of scleractinian (stony) corals are difficult to infer given the existence of few diagnostic characters and pervasive phenotypic plasticity. A previous study of Hawaiian Montipora (Scleractinia: Acroporidae) based on five partial mitochondrial and two nuclear genes revealed the existence of a species complex, grouping one of the rarest known species (M. dilatata, which is listed as Endangered by the International Union for Conservation of Nature - IUCN) with widespread corals of very different colony growth forms (M. flabellata and M. cf. turgescens). These previous results could result from a lack of resolution due to a limited number of markers, compositional heterogeneity or reflect biological processes such as incomplete lineage sorting (ILS) or introgression. Results All 13 mitochondrial protein-coding genes from 55 scleractinians (14 lineages from this study) were used to evaluate if a recent origin of the M. dilatata species complex or rate heterogeneity could be compromising phylogenetic inference. Rate heterogeneity detected in the mitochondrial data set seems to have no significant impacts on the phylogenies but clearly affects age estimates. Dating analyses show different estimations for the speciation of M. dilatata species complex depending on whether taking compositional heterogeneity into account (0.8 [0.05–2.6] Myr) or assuming rate homogeneity (0.4 [0.14–0.75] Myr). Genomic data also provided evidence of introgression among all analysed samples of the complex. RADseq data indicated that M. capitata colour morphs may have a genetic basis. Conclusions Despite the volume of data (over 60,000 SNPs), phylogenetic relationships within the M. dilatata species complex remain unresolved most likely due to a recent origin and ongoing introgression. Species delimitation with genomic data is not concordant with the current taxonomy, which does not reflect the true diversity of this group. Nominal species within the complex are either undergoing a speciation process or represent ecomorphs exhibiting phenotypic polymorphisms.info:eu-repo/semantics/publishedVersio

A Coalescent Sampler Successfully Detects Biologically Meaningful Population Structure Overlooked by F‐Statistics

Assessing the geographic structure of populations has relied heavily on Sewell Wright\u27s F‐statistics and their numerous analogues for many decades. However, it is well appreciated that, due to their nonlinear relationship with gene flow, F statistics frequently fail to reject the null model of panmixia in species with relatively high levels of gene flow and large population sizes. Coalescent genealogy samplers instead allow a model‐selection approach to the characterization of population structure, thereby providing the opportunity for stronger inference. Here, we validate the use of coalescent samplers in a high gene flow context using simulations of a stepping‐stone model. In an example case study, we then re‐analyze genetic datasets from 41 marine species sampled from throughout the Hawaiian archipelago using coalescent model selection. Due to the archipelago\u27s linear nature, it is expected that most species will conform to some sort of stepping‐stone model (leading to an expected pattern of isolation by distance), but F‐statistics have only supported this inference in ~10% of these datasets. Our simulation analysis shows that a coalescent sampler can make a correct inference of stepping‐stone gene flow in nearly 100% of cases where gene flow is ≤100 migrants per generation (equivalent to FST = 0.002), while F‐statistics had mixed results. Our re‐analysis of empirical datasets found that nearly 70% of datasets with an unambiguous result fit a stepping‐stone model with varying population sizes and rates of gene flow, although 37% of datasets yielded ambiguous results. Together, our results demonstrate that coalescent samplers hold great promise for detecting weak but meaningful population structure, and defining appropriate management units

Population genetic structure between Yap and Palau for the coral Acropora hyacinthus

Information on connectivity is becoming increasingly in demand as marine protected areas are being designed as an integral part of a network to protect marine resources at the ecosystem level. Larval dispersal and population structure, however, remain very difficult to assess. Here, we tested the predictions of a detailed oceanographic connectivity model of larval dispersal and coral recruitment within Palau and between Palau and Yap, which was developed to support the review of the existing network of marine protected areas in Palau. We used high throughput microsatellite genotyping of the coral Acropora hyacinthus to characterize population genetic structure. Pairwise F ′ ST values between Palau and Yap (0.10), Palau and Ngulu (0.09) and Yap and Ngulu (0.09) were all significant and similar to pairwise F ′ ST values of sites within Palau (0.02–0.12) and within Yap (0.02–0.09) highlighting structure at island scale and indicating that recruitment may be even more localized than previously anticipated. A bottleneck test did not reveal any signs of a founder effect between Yap and Palau. Overall, the data supports the idea that recovery of A. hyacinthus in Palau did not come exclusively from a single source but most likely came from a combination of areas, including sites within Palau. In light of these results there seems to be very little connectivity around the barrier reef and management recommendation would be to increase the number or the size of MPAs within Palau

High-Frequency Temperature Variability Mirrors Fixed Differences in Thermal Limits of the Massive Coral \u3ci\u3ePorites lobata\u3c/i\u3e

Spatial heterogeneity in environmental characteristics can drive adaptive differentiation when contrasting environments exert divergent selection pressures. This environmental and genetic heterogeneity can substantially influence population and community resilience to disturbance events. Here, we investigated corals from the highly variable back-reef habitats of Ofu Island in American Samoa that thrive in thermal conditions known to elicit widespread bleaching and mortality elsewhere. To investigate the relative importance of acclimation versus site of origin in shaping previously observed differences in coral tolerance limits at Ofu Island, specimens of the common Indo-Pacific coral Porites lobata from locations with differing levels of thermal variability were acclimated to low and high thermal variation in controlled common garden aquaria. Overall, there were minimal effects of the acclimation exposure. Corals native to the site with the highest level of daily variability grew fastest, regardless of acclimation treatment. When exposed to lethal thermal stress, corals native to both variable sites contained elevated levels of heat shock proteins and maintained photosynthetic performance for 1–2 days longer than corals from the stable environment. Despite being separated by \u3c5 \u3ekm, there was significant genetic differentiation among coral colonies (FST=0.206, PCladocopium sp. (ITS type C15). Our study demonstrates consistent signatures of adaptation in growth and stress resistance in corals from naturally thermally variable habitats, suggesting that differences in the amount of thermal variability may be an important contributor to adaptive differentiation in reef-building corals

Gateways to Hawai‘i: Genetic Population Structure of the Tropical Sea Cucumber Holothuria atra

Holothuria atra is one of the most common and widest ranging tropical, coral reef sea cucumbers in the world, and here we examine population genetic structure based on mitochondrial COI to aid in determining the appropriate scale for coral reef management. Based on SAMOVA, AMOVA and BARRIER analyses, we show that despite its large range, H. atra has hierarchical, fine-scale population structure driven primarily by between-archipelago barriers, but with significant differences between sites within an archipelago as well. Migrate analyses along with haplotype networks and patterns of haplotype diversity suggest that Hawai‘i and Kingman reef are important centers of the genetic diversity in the region rather than an evolutionary dead-end for migrants from the Indo-Pacific. Finally we show that for H. atra Kingman Reef is the most likely stepping stone between Hawai‘i and the rest of the Pacific, not Japan or Johnston Atoll as previously presumed. Based on our data, Johnston Atoll can instead be seen as an outpost of the Northwestern Hawaiian Islands rather than a gateway to the Hawaiian Archipelago

The Scope of Published Population Genetic Data for Indo-Pacific Marine Fauna and Future Research Opportunities in the Region

Marine biodiversity reaches its pinnacle in the tropical Indo-Pacific region, with high levels of both species richness and endemism, especially in coral reef habitats. While this pattern of biodiversity has been known to biogeographers for centuries, causal mechanisms remain enigmatic. Over the past 20 yrs, genetic markers have been employed by many researchers as a tool to elucidate patterns of biodiversity above and below the species level, as well as to make inferences about the underlying processes of diversification, demographic history, and dispersal. In a quantitative, comparative framework, these data can be synthesized to address questions about this bewildering diversity by treating species as “replicates.” However, the sheer size of the Indo-Pacific region means that the geographic and genetic scope of many species’ data sets are not complementary. Here, we describe data sets from 116 Indo-Pacific species (108 studies). With a mind to future synthetic investigations, we consider the strengths and omissions of currently published population genetic data for marine fauna of the Indo-Pacific region, as well as the geographic and taxonomic scope of the data, and suggest some ways forward for data collection and collation

Modeled larval connectivity of a multi-species reef fish and invertebrate assemblage off the coast of Moloka‘i, Hawai‘i

We use a novel individual-based model (IBM) to simulate larval dispersal around the island of Moloka‘i in the Hawaiian Archipelago. Our model uses ocean current output from the Massachusetts Institute of Technology general circulation model (MITgcm) as well as biological data on four invertebrate and seven fish species of management relevance to produce connectivity maps among sites around the island of Moloka‘i. These 11 species span the range of life history characteristics of Hawaiian coral reef species and show different spatial and temporal patterns of connectivity as a result. As expected, the longer the pelagic larval duration (PLD), the greater the proportion of larvae that disperse longer distances, but regardless of PLD (3–270 d) most successful dispersal occurs either over short distances within an island (<30 km) or to adjacent islands (50–125 km). Again, regardless of PLD, around the island of Moloka‘i, connectivity tends to be greatest among sites along the same coastline and exchange between northward, southward, eastward and westward-facing shores is limited. Using a graph-theoretic approach to visualize the data, we highlight that the eastern side of the island tends to show the greatest out-degree and betweenness centrality, which indicate important larval sources and connectivity pathways for the rest of the island. The marine protected area surrounding Kalaupapa National Historical Park emerges as a potential source for between-island larval connections, and the west coast of the Park is one of the few regions on Moloka‘i that acts as a net larval source across all species. Using this IBM and visualization approach reveals patterns of exchange between habitat regions and highlights critical larval sources and multi-generational pathways to indicate priority areas for marine resource managers