Severe disturbances can substantially alter eco-evolutionary processes and dynamics. While the impacts of catastrophic events on the biophysical attributes of communities are sometimes assessed, their effects on the genetic patterns of species remain poorly understood. To characterize how severe disturbances impact species at the molecular level, we examined the effects of the most energetic North Atlantic hurricane season in 50 years on the genetic diversity and structure of a dispersal-limited isopod, Gnathia marleyi. We sequenced a portion of the cytochrome oxidase I gene for 432 gnathiids, collected from six localities, ranging from western Puerto Rico to St John, US Virgin Islands. Importantly, multiple years of pre-hurricane sample collection allowed us to characterize temporal genetic patterns under undisturbed conditions and detect the changes subsequent to the 2017 hurricanes. Our results revealed no change to genetic diversity or structure for the years prior to the 2017 hurricanes, with genetic structure occurring at the local and regional levels, with three main clusters corresponding to Southwest Puerto Rico, East Puerto Rico, and the US Virgin Islands. However, directly following the 2017 hurricanes, genetic diversity increased at five of the six sampled localities. Additionally, we found a clear homogenizing effect prompted by increased shared genetic diversity among geographically distant regions and sites that resulted in substantially decreased among-region and among-site differentiation. Our work shows that severe disturbances caused by major tropical hurricanes facilitate gene-flow and increase overall genetic diversity and population admixture of dispersal limited coral reef species, potentially impacting the ecology and evolution of a key regional endemic.

No abstract

Assessing the importance of intrinsic and extrinsic factors that shape the spatial distribution of genetic diversity of symbionts has been a topic of debate for decades. While host-mediated dispersal is an important driver of gene flow in many terrestrial metazoan symbionts, few studies have identified the drivers of symbiont genetic differentiation in the marine realm, where habitats are comparatively more homogeneous and long-distance dispersal is common. In the present study, we perform a meta-analysis of existing studies examining symbiont spatial genetic diversity to determine which symbiont- and host-related traits shape the patterns of genetic differentiation of metazoan symbionts, while also considering technical aspects of each study. Specifically, we wanted to assess the influence of biological traits and/or technical aspects in (1) detecting genetic differentiation in marine symbionts, and (2) shaping the minimum spatial scale at which genetic differentiation was detected. By assessing genetic diversity of mtDNA markers, we found that the spatial scale at which studies are conducted was a crucial predictor of both detection of genetic structure and scale at which differentiation of marine symbionts was detected. Symbiont-based traits did not influence genetic structure, however, host-mediated dispersal was the only biological trait that shaped genetic structure of marine symbionts by influencing the spatial distribution at which differentiation was detected.

Specialist species have evolved to fill narrow niches but are especially susceptible to environmental change. With sufficient functional redundancy, ecosystem services can persist without specialists. Grooming behaviors are common in both terrestrial and aquatic organisms. However, in aquatic systems there is a heavy reliance on intraspecific mutualisms where specialist species groom or “clean” parasites off host fishes. Here, we sampled the gut contents of 709 fishes, representing 61 species and including both cleaner and non-cleaner fishes, to compare their consumption of gnathiid isopods, the most common fish ectoparasites. We found that cleaner fishes eat significantly more gnathiids, and eat them more frequently, compared to non-cleaner fishes. Our results highlight the importance of both dedicated and facultative cleaners as consumers of ectoparasites and show that their role cannot be supplanted by generalist consumers. Furthermore, we suggest that different cleaner species act as complementary rather than redundant specialists.