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opencc-zeroMar 2020View details →

Data from: Inbreeding shapes the evolution of marine invertebrates

Inbreeding is a potent evolutionary force shaping the distribution of genetic variation within and among populations of plants and animals. Yet, our understanding of the forces shaping the expression and evolution of non-random mating in general, and inbreeding in particular, remains remarkably incomplete. Most research on plant mating systems focuses on self-fertilization and its consequences for automatic selection, inbreeding depression, purging, and reproductive assurance, whereas studies of animal mating systems have often assumed that inbreeding is rare, and that natural selection favors traits that promote outbreeding. Given that many sessile and sedentary marine invertebrates and marine macroalgae share key life-history features with seed plants (e.g., low mobility, modular construction, and the release of gametes into the environment), their mating systems may be similar. Here, we show that published estimates of inbreeding coefficients (FIS) for sessile and sedentary marine organisms are similar and at least as high as noted in terrestrial seed plants. We also found that variation in FIS within invertebrates is related to the potential to self-fertilize, disperse, and choose mates. The similarity of FIS for these organismal groups suggests that inbreeding could play a larger role in the evolution of sessile and sedentary marine organisms than is currently recognized. Specifically, associations between traits of marine invertebrates and FIS suggest that inbreeding could drive evolutionary transitions between hermaphroditism and separate sexes, direct development and multiphasic life cycles, and external and internal fertilization.

opencc-zeroDec 2012View details →

Data from: Going where traditional markers have not gone before: utility of and promise for RAD-sequencing in marine invertebrate phylogeography and population genomics

Characterization of large numbers of single-nucleotide polymorphisms (SNPs) throughout a genome has the power to refine the understanding of population demographic history and to identify genomic regions under selection in natural populations. To this end, population genomic approaches that harness the power of next-generation sequencing to understand the ecology and evolution of marine invertebrates represent a boon to test long-standing questions in marine biology and conservation. We employed restriction-site-associated DNA sequencing (RAD-seq) to identify SNPs in natural populations of the sea anemone Nematostella vectensis, an emerging cnidarian model with a broad geographic range in estuarine habitats in North and South America, and portions of England. We identified hundreds of SNP-containing tags in thousands of RAD loci from 30 barcoded individuals inhabiting four locations from Nova Scotia to South Carolina. Population genomic analyses using high-confidence SNPs resulted in a highly-resolved phylogeography, a result not achieved in previous studies using traditional markers. Plots of locus-specific FST against heterozygosity suggest that a majority of polymorphic sites are neutral, with a smaller proportion suggesting evidence for balancing selection. Loci inferred to be under balancing selection were mapped to the genome, where 90% were located in gene bodies, indicating potential targets of selection. The results from analyses with and without a reference genome supported similar conclusions, further highlighting RAD-seq as a method that can be efficiently applied to species lacking existing genomic resources. We discuss the utility of RAD-seq approaches in burgeoning Nematostella research as well as in other cnidarian species, particularly corals and jellyfishes, to determine phylogeographic relationships of populations and identify regions of the genome undergoing selection.

opencc-zeroDec 2010View details →

Data from: Vision and the diversification of Phanerozoic marine invertebrates

Identifying biological traits that promote evolutionary success is fundamental for understanding biodiversity dynamics and for assessing the evolutionary response of organisms to global change. We tested the hypothesis that image-forming eyes have contributed to the diversification of taxa in the geological past. Using fossil occurrences in the Paleobiology Database, we analyzed the diversity and evolutionary rates of more than 17,000 Phanerozoic genera of marine invertebrates living on or above the shallow-water seafloor according to their visual capabilities. Analysis of the complete data set shows a peak in the proportional diversity of sighted genera early in the Phanerozoic, and their continuance at a relatively low and stable level after the Ordovician. As an explanation of this pattern we suggest that selection pressure to develop eyes rose in the Cambrian, and that behavioral constraints had a balancing effect thereafter. In contrast to the pooled data, a clade-level study of those subgroups that contain both sighted and blind genera revealed that—in trilobites, all epifaunal bivalves, pectinoid bivalves, gastropods, and echinoderms—sighted genera diversified more strongly than blind genera. This difference is controlled by significantly raised extinction rates of blind genera. These more finely resolved patterns support the hypothesis that good vision is a key trait that promoted preferential diversification.

opencc-zeroDec 2012View details →

Data from: Controls on niche stability in geologic time Congruent responses to biotic and abiotic environmental changes among Cincinnatian (Late Ordovician) marine invertebrates

The set of environmental conditions under which a taxon can survive and maintain viable populations, known as the ecological niche, is a fundamental determinant of a taxon's distribution. Because of the central importance of ecological niches, they have been assumed to remain relatively stable during intervals of morphological stasis. However, the assumption of niche stability has rarely been tested directly with fossil data spanning multiple temporal intervals. Thus, the conditions under which this assumption is likely to be accurate are not well understood. In this study, we use ecological niche modeling (ENM) to reconstruct the ecological niche for 11 genera of marine benthos (crinoids, trilobites, molluscs, bryozoans, and corals) from the Type Cincinnatian Series (Late Ordovician, Katian Stage) across nine temporal intervals spanning approximately three million years. This interval includes both abiotic environmental change (gradual sea-level fall) and biotic change (rapid pulses of the Richmondian Invasion), thus allowing the relative effect of different environmental perturbations to be constrained. A previous symmetrical analysis of niche stability of brachiopod species recovered an increase in niche evolution following the Richmondian Invasion. Herein we test the generality of the brachiopod pattern within the community. Niche stability was evaluated in geographic space, ecological space, and niche parameter space. Niche stability varied through time; during the Pre-Invasion interval, taxa exhibited niche stability during gradual shallowing of sea level in the basin, whereas niche evolution became more common during the Richmondian Invasion. Taxa adjusted to the increased competition by altering aspects of their niche. Notably, surviving taxa contracted their niche into a subset of their previous niche parameters. This represents an adaptive response to increased competition for resources with the newly established invader taxa, and it was employed most successfully by generalist taxa. Patterns of niche evolution were congruent between clades, among feeding styles, and across taxonomic levels.

opencc-zeroDec 2012View details →

Data from: Vertical distribution of marine invertebrate larvae in response to thermal stratification in the laboratory

We investigated the effect of the presence of an experimentally generated thermocline on the vertical distribution of larval Strongylocentrotus droebachiensis, Asterias rubens and Argopecten irradians. Vertical distributions were recorded over 90 min in rectangular plexiglass thermocline chambers designed to regulate the temperature of a central observation compartment to the desired values. The temperature in the bottom water layer (B) and the temperature difference between layers (ΔT) were manipulated in an orthogonal design. We used, for S. droebachiensis: 4 levels of ΔT (0, 3, 6 and 12 °C) and 3 levels of B (3, 6 and 9 °C); for A. rubens: 3 levels ΔT (0, 6 and 12 °C) and 2 levels of B (6 and 12 °C); and for A. irradians: 3 levels of ΔT (0, 5 and 11 °C) and 2 levels of B (5 and 11 °C). The difference in temperature between water layers did not affect the vertical distribution of echinoderms consistently, while the distribution of A. irradians was limited to the bottom layer when any thermal stratification was present regardless of strength. Our results suggest that the vertical position of larvae of S. droebachiensis and A. rubens is related to the temperatures of the surface layer and that the presence alone or the steepness of the thermocline has less influence on their distribution. Consequently, in the field, echinoderm larvae would aggregate at the surface unless temperature extremes were encountered. In contrast, the position of A. irradians was limited to the bottom layer in the presence of a thermocline of at least 5 °C (the shallowest used in our study). Such thermoclines are common in a natural setting and could affect the vertical distribution and horizontal dispersal of larvae by acting as a barrier to vertical migration.

opencc-zeroDec 2016View details →

Data from: Genotype by sequencing identifies natural selection as a driver of intraspecific divergence in Atlantic populations of the high dispersal marine invertebrate, Macoma petalum

Mitochondrial DNA analyses indicate that the Bay of Fundy population of the intertidal tellinid bivalve Macoma petalum is genetically divergent from coastal populations in the Gulf of Maine and Nova Scotia. To further examine the evolutionary forces driving this genetic break, we performed double digest genotype by sequencing (GBS) to survey the nuclear genome for evidence of both neutral and selective processes shaping this pattern. The resulting reads were mapped to a partial transcriptome of its sister species, M. balthica, to identify single nucleotide polymorphisms (SNPs) in protein-coding genes. Population assignment tests, principle components analyses, analysis of molecular variance, and outlier tests all support differentiation between the Bay of Fundy genotype and the genotypes of the Gulf of Maine, Gulf of St. Lawrence, and Nova Scotia. Although both neutral and non-neutral patterns of genetic subdivision were significant, genetic structure among the regions was nearly 20 times higher for loci putatively under selection, suggesting a strong role for natural selection as a driver of genetic diversity in this species. Genetic differences were the greatest between the Bay of Fundy and all other population samples, and some outlier proteins were involved in immunity-related processes. Our results suggest that in combination with limited gene flow across the mouth of the Bay of Fundy, local adaptation is an important driver of intraspecific genetic variation in this marine species with high dispersal potential.

opencc-zeroDec 2015View details →

Data from: Recovery from hybrid breakdown in a marine invertebrate is faster, stronger and more repeatable under environmental stress

Understanding how environmental stress alters the consequences of hybridization is important, because the rate of hybridization and the likelihood of hybrid speciation both appear elevated in harsh, disturbed or marginal habitats. We assessed fitness, morphometrics and molecular genetic composition over 14 generations of hybridization between two highly divergent populations of the marine copepod Tigriopus californicus. Replicated, experimental hybrid populations in both control and high salinity conditions showed a decline in fitness, followed by a recovery. Recovery was faster in the salinity stress treatment, returning to parental levels up to two generations earlier than in the control. This recovery was stable in the high salinity treatment, while in the control treatment fitness dropped back below parental levels at the final time point. Recovery in the high salinity treatment was also stronger in terms of competitive fitness and heat shock tolerance. Finally, consequences of hybridization were more repeatable under salinity stress, where among-replicate variance for survivorship and molecular genetic composition was lower than in the control treatment. In a system with low effective population sizes (estimates ranged from 17 to 63), where genetic drift might be expected to be the predominate force, strong selection under harsh environmental conditions apparently promoted faster, stronger and more repeatable recovery from depressed hybrid fitness.

FIGURE 9. Asterocheres siphonatus Giesbrecht, 1897, female. A, leg 5. B, leg 5 in Asterocherids (Copepoda: Siphonostomatoida) associated with marine invertebrates in the Strait of Gibraltar

FIGURE 9. Asterocheres siphonatus Giesbrecht, 1897, female. A, leg 5. B, leg 5, detail of the subterminal seta. C, antennule, seta with a circlet of cuticular denticles at its tip.

FIGURE 5 in Asterocherids (Copepoda: Siphonostomatoida) associated with marine invertebrates in the Strait of Gibraltar

FIGURE 5. Asterocheres minutus (Claus, 1889), female. A, dorsal view. B, cephalic appendages C, antenna. D, mandible, E, maxillule. F, maxilla.

FIGURE 2. Asterocheres tarifensis n in Asterocherids (Copepoda: Siphonostomatoida) associated with marine invertebrates in the Strait of Gibraltar

FIGURE 2. Asterocheres tarifensis n. sp., female. A, mandible. B, maxillule C, maxilla. D, maxilliped.

FIGURE 1. Asterocheres tarifensis n in Asterocherids (Copepoda: Siphonostomatoida) associated with marine invertebrates in the Strait of Gibraltar

FIGURE 1. Asterocheres tarifensis n. sp., female. A, dorsal view. B, urosome, dorsal view. C, urosome, ventral view. D, antenna. E, antennule.

FIGURE 7. Asterocheres siphonatus Giesbrecht, 1897, female. A, mandible. B, maxillule C, maxilla. D in Asterocherids (Copepoda: Siphonostomatoida) associated with marine invertebrates in the Strait of Gibraltar

FIGURE 7. Asterocheres siphonatus Giesbrecht, 1897, female. A, mandible. B, maxillule C, maxilla. D, maxilliped.

FIGURE 6. Asterocheres siphonatus Giesbrecht, 1897, female. A, dorsal view. B in Asterocherids (Copepoda: Siphonostomatoida) associated with marine invertebrates in the Strait of Gibraltar

FIGURE 6. Asterocheres siphonatus Giesbrecht, 1897, female. A, dorsal view. B, urosome, dorsal view. C, urosome,ventralview. D, antenna. E, antennule.

opencc-zeroJun 2021View details →

Genomic evidence for speciation with gene flow in broadcast spawning marine invertebrates

How early stages of speciation in free-spawning marine invertebrates proceeds is poorly understood. The Western Pacific abalones, Hatiois discus, H. madaka, and H. gigantea occur in sympatry with shared breeding season and are capable of producing viable F1 hybrids in spite of being ecologically differentiated. Population genomic analyses revealed that although the three species are genetically distinct, there is evidence for historical and ongoing gene flow among these species. Evidence from demographic modeling suggests that reproductive isolation among the three species started to build in allopatry and have proceeded with gene flow, possibly driven by ecological selection. We identified 27 differentiation islands between the closely related H. discus and H. madaka characterized by high FST and dA, but not high dXY values, as well as high genetic diversity in one H. madaka population. These genomic signatures suggest differentiation driven by recent ecological divergent selection in presence of gene flow outside of the genomic islands of differentiation. The differentiation islands showed low polymorphism in H. gigantea, and both high FST, dXY, and dA values between H. discus and H. gigantea, as well as between H. madaka and H. gigantea. Collectively, the western Pacific abalones appear to occupy the early stages speciation continuum, and the differentiation islands associated with ecological divergence among the abalones do not appear to have acted as barrier loci to gene flow in the younger divergences but appear to do so in older divergences.

opencc-zeroJun 2021View details →

Negative relationship between thermal tolerance and plasticity in tolerance emerges during experimental evolution in a widespread marine invertebrate

Whether populations can adapt to predicted climate change conditions, and how rapidly, are critical questions for the management of natural systems. Experimental evolution has become an important tool to answer these questions. In order to provide useful, realistic insights into the adaptive response of populations to climate change, there needs to be careful consideration of how genetic differentiation and phenotypic plasticity interact to generate observed phenotypic changes. We exposed three populations of the widespread copepod Acartia tonsa (Crustacea) to chronic, sub-lethal temperature selection for 15 generations. We generated thermal survivorship curves at regular intervals both during and after this period of selection to track the evolution of thermal tolerance. Using reciprocal transplants between ambient and warming conditions, we also tracked changes in the strength of phenotypic plasticity in thermal tolerance. We observed significant increases in thermal tolerance in the warming lineages, while plasticity in thermal tolerance was strongly reduced.

Figure 7 in A zoologist's perspective on Robert Hooke's Micrographia (1665) studies of marine and terrestrial invertebrates, and his contemplations on invertebrate "generation" and mutability

Figure 7. Several individuals of the free-living nematode Turbatrix aceti (Müller) (Nemata: Secernentea: Rhabdita: Panagrolaimidae). Engraving reproduced by permission of the Rare Book and Manuscript Library of the University of Pennsylvania.

Figure 6 in A zoologist's perspective on Robert Hooke's Micrographia (1665) studies of marine and terrestrial invertebrates, and his contemplations on invertebrate "generation" and mutability

Figure 6. Dorsal and ventral aspects of an astigmatid mite of the genus Tyrophagus (Chelicerata: Arachnida: Acari), probably T. longior (Gervais). Engraving reproduced by permission of the Rare Book and Manuscript Library of the University of Pennsylvania.

Figure 5. A in A zoologist's perspective on Robert Hooke's Micrographia (1665) studies of marine and terrestrial invertebrates, and his contemplations on invertebrate "generation" and mutability

Figure 5. A pseudoscorpion, Chelifer cancroides (L.) (Chelicerata: Arachnida: Pseudoscorpionida). Engraving reproduced by permission of the Rare Book and Manuscript Library of the University of Pennsylvania.

Figure 4 in A zoologist's perspective on Robert Hooke's Micrographia (1665) studies of marine and terrestrial invertebrates, and his contemplations on invertebrate "generation" and mutability

Figure 4. An oribatid mite of the family Oribatulidae, very likely Phauloppia lucorum (Koch). Engraving reproduced by permission of the Rare Book and Manuscript Library of the University of Pennsylvania.

Figure 3 in A zoologist's perspective on Robert Hooke's Micrographia (1665) studies of marine and terrestrial invertebrates, and his contemplations on invertebrate "generation" and mutability

Figure 3. Dorsal and ventral aspects of the same male individual of a harvestman (Arthropoda: Chelicerata: Opiliones), most likely Leiobunum rotundum (Latreille). Engraving reproduced by permission of the Rare Book and Manuscript Library of the University of Pennsylvania.