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Strong genetic structure in a widespread estuarine crab: A test of potential versus realized dispersal

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2020-10-27

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"Aim: Genetic structure has proven difficult to predict for marine and estuarine species with multi-day pelagic larval durations, since many disperse far less than expected based on passive transport models. In such cases, the gap between potential and realized dispersal may result from larval behaviors that evolved to facilitate retention and settlement in favorable environments. Behavior is predicted to play a particularly key role in structuring truly estuarine species, which often moderate their behavior to remain within their natal estuaries. In such systems, this restricted dispersal may lead to high divergence, local adaptation, and eventual speciation across their range. Here, we test whether a geographically widespread estuarine crab, known to have behavior promoting larval retention, exhibits high population structure despite a 2-4 week larval duration. Location: Atlantic and Gulf Coasts of North America Taxon: White-fingered mud crab, Rhithropanopeus harrisii Methods: Population genomic analyses across nine estuaries from New Hampshire to Louisiana using 12,638 transcriptome-derived SNPs. Results: We found highly differentiated genetic signatures among all nine estuaries, separated by 200-5,000 km of coastline. Estimates of gene flow suggest that migration is low and largely symmetrical between sites. We also observed deep phylogenetic divides corresponding to major biogeographic breaks. Main conclusions: These results indicate substantial and longstanding constraints to dispersal in the species’ native range, likely arising from the emergence of geological and oceanographic barriers and sustained by behavior that promotes estuarine retention during larval development. This work supports the idea that larval behavior promoting estuarine retention can be reflected in substantial genetic structure even in species with multi-week pelagic larval durations. Such behavior-restricted dispersal has implications for predicting adaptation and spread in estuarine species, many of which have been introduced outside their native ranges."

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estuarine retention, Larval behavior, larval dispersal

DOI

https://doi.org/10.5061/dryad.qnk98sfd1

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Smithsonian Institute for Biodiversity Genomics: Biodiversity Genomics Postdoctoral Fellowship; Smithsonian Institute for Biodiversity Genomics: Biodiversity Genomics sequencing award; Smithsonian Institute for Biodiversity Genomics: Biodiversity Genomics Postdoctoral Fellowship

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Item type:Publication, Access status: Open Access ,
Recent introductions reveal differential susceptibility to parasitism across an evolutionary mosaic
(2019-08-14) Tepolt, Carolyn K.; Darling, John A.; Blakeslee, April; Fowler, Amy E.; Torchin, Mark E.; Miller, A. Whitman; Ruiz, Gregory M.
Parasitism can represent a potent agent of selection, and introduced parasites have the potential to substantially alter their new hosts' ecology and evolution. While sig‐ nificant impacts have been reported for parasites that switch to new host species, the effects of macroparasite introduction into naïve populations of host species with which they have evolved remain poorly understood. Here, we investigate how the estuarine white‐fingered mud crab (Rhithropanopeus harrisii) has adapted to parasit‐ ism by an introduced rhizocephalan parasite (Loxothylacus panopaei) that castrates its host. While the host crab is native to much of the East and Gulf Coasts of North America, its parasite is native only to the southern end of this range. Fifty years ago, the parasite invaded the mid‐Atlantic, gradually expanding through previously naïve host populations. Thus, different populations of the same host species have expe‐ rienced different degrees of historical interaction (and thus potential evolutionary response time) with the parasite: long term, short term, and naïve. In nine estuaries across this range, we examined whether and how parasite prevalence and host sus‐ ceptibility to parasitism differs depending on the length of the host's history with the parasite. In field surveys, we found that the parasite was significantly more preva‐ lent in its introduced range (i.e., short‐term interaction) than in its native range (long‐ term interaction), a result that was also supported by a meta‐analysis of prevalence data covering the 50 years since its introduction. In controlled laboratory experi‐ ments, host susceptibility to parasitism was significantly higher in naïve hosts than in hosts from the parasite's native range, suggesting that host resistance to parasitism is under selection. These results suggest that differences in host–parasite historical interaction can alter the consequences of parasite introductions in host populations. As anthropogenically driven range shifts continue, disruptions of host–parasite evo‐ lutionary relationships may become an increasingly important driver of ecological and evolutionary change.

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