Two recent Blakeslee lab publications: one featuring zombie crabs and salinity, and the other a comparative phylogeography of two Littorina snails (JUNE 2021)
It was very exciting that two publications came out of my lab this summer! The first is a lab-wide projecting exploring the influence of salinity gradients on parasite prevalence in mud crabs of an invasive body-snatching parasite. The second is an international trans-Atlantic collaboration of two related Littorina snail species that show strong differences in their phylogeographies, partly due to opposing reproductive strategies. See the titles, authors, abstracts, and links below.
(1) Invasion of the body snatchers: the role of parasite introduction in host distribution and response to salinity in invaded estuaries.
Blakeslee AMH, Pochtar DL, Fowler AE, Moore CS, Lee TS, Barnard RB, Swanson KL, Lukas LC, Ruocchio M, Torchin ME, Miller AW, Ruiz GM, Tepolt CK (2021) Proceedings of the Royal Society Series B Biology. 288: 20210703.
Abstract: In dynamic systems, organisms are faced with variable selective forces that may impose trade-offs. In estuaries, salinity is a strong driver of organismal diversity, while parasites shape species distributions and demography. We tested for trade-offs between low-salinity stress and parasitism in an invasive castrating parasite and its mud crab host along salinity gradients of two North Carolina rivers. We performed field surveys every six to eight weeks over 3 years to determine factors influencing parasite prevalence, host abundance, and associated taxa diversity. We also looked for signatures of low-salinity stress in the host by examining its response (time-to-right and gene expression) to salinity. We found salinity and temperature significantly affected parasite prevalence, with low-salinity sites (less than 10 practical salinity units (PSU)) lacking infection, and populations in moderate salinities at warmer temperatures reaching prevalence as high as 60%. Host abundance was negatively associated with parasite prevalence. Host gene expression was plastic to acclimation salinity, but several osmoregulatory and immune-related genes demonstrated source-dependent salinity response. We identified a genetic marker that was strongly associated with salinity against a backdrop of no neutral genetic structure, suggesting possible selection on standing variation. Our study illuminates how selective trade-offs in naturally dynamic systems may shape host evolutionary ecology.
(2) Population structure and phylogeography of two North Atlantic Littorina species with contrasting larval development.
Blakeslee AMH, Miller AW, Ruiz GM, Johannesson K, André C, Panova M (2021). Marine Biology. 168: 1-16. https://doi.org/10.1007/s00227-021-03918-8
Abstract: Phylogeography provides insights into how historical and contemporary processes influence the genetic structure and gene flow in marine organisms around the globe. In benthic marine invertebrates, a species’ reproductive strategy can strongly impact phylogeographic patterns and distribution, with some direct-developing (non-planktonic) dispersers demonstrating strong genetic structure but also broad geographic spread. While seemingly paradoxical, past work has shown ovoviviparous species, like Littorina saxatilis, can be more successful colonizers of remote locations than species with planktonic larvae, like L. littorea. Both Littorina species overlap in much of their North Atlantic ranges but have different colonization histories: L. saxatilis is native on both North Atlantic coasts and islands, and L. littorea is native to the eastern Atlantic but introduced to the west. Using an extensive mitochondrial dataset (1236 sequences; 85 sites), we examined how their opposing reproductive strategies correspond to their distributions and phylogeographies. Littorina saxatilis exhibited a heterogeneous genetic structure reflecting post-glacial recolonization from multiple refugial sites, while L. littorea had a homogeneous structure with a post-glacial history characterized by recolonization from one main refugial area in the northeast Atlantic. Further, haplotype diversity was significantly depressed in northwest Atlantic L. littorea populations, signifying a strong bottleneck characteristic of a human-mediated introduction. In contrast, haplotype diversity in L. saxatilis was similar between the two regions, demonstrating long-term history on both coasts. Thus, our study suggests contrasting life-history characteristics were a major structuring force in the phylogeographic patterns of these related species following large-scale disturbances (natural and anthropogenic) that compel contraction and redistribution over large areas.