Figure 2-1 - uploaded by Greer A. Dolby
Content may be subject to copyright.
Sample collection and bathymetric map. Bathymetry is contoured at 10-meter intervals from 0 to 140 meters below present sea level (orange to dark blue, respectively). White markers note sample sites for fish species where: G-Gillichthys mirabilis, Q-Quietula y-cauda, F-Fundulus parvipinnis. Triangle denotes the Cabo Colonet region, which our models predict supported habitat ~10 thousand years ago (kya), but does not today. Note the distribution of offshore islands, whose sizes increased with lowered sea level.
Source publication
Over 150 years of investigation has yielded knowledge of the patterns and mechanisms of biological evolution. Yet rarely do such studies integrate the physical mechanisms that drive this evolution on a timescale that is biologically meaningful. Without integrating physical and biological processes, we risk overlooking the co-evolutionary nature of...
Similar publications
Temperature is a key controlling variable from subcellular to ecosystem scales. Thus, climatic warming is expected to have broad impacts, especially in economically and ecologically valuable systems such as estuaries. The heavily managed upper San Francisco Estuary (SFE) supplies water to millions of people and is home to fish species of high conse...
Citations
... For Pacific sites, we ran DFA using variables previously found to predict the distribution of these fishes (maximum polygon area and summed area; Dolby et al., 2016) anterior to the caudal peduncle and amplified the mitochondrial control region (mtCR) for all three species and cytochrome B (cyt B) for Q. y-cauda and G. mirabilis using published primers (Iwata et al., 2000;Lee, Conroy, Howell, & Kocher, 1995) and standard protocols (Ellingson et al., 2014;Supporting Information). Individuals were genotyped at the UCLA GenoSeq Core (Dolby, 2015;Dolby et al., 2016). Gulf samples post hoc to assess the relative likelihood of a twopopulation versus one-population model using the ΔK metric (Evanno et al., 2005). ...
Plate tectonics and sediment processes control regional continental shelf topography. We examine the genetic consequences of how glacial-associated sea-level change interacted with variable near-shore topography since the last glaciation. We reconstructed the size and distribution of areas suitable for tidal estuary formation from the Last Glacial Maximum, ~20 thousand years ago, to present from San Francisco, California, USA (~38 °N) to Reforma, Sinaloa, Mexico (~25 °N). We assessed range-wide genetic structure and diversity of three co-distributed tidal estuarine fishes (California Killifish, Shadow Goby, Longjaw Mudsucker) along ~4,600 km using mitochondrial control region and cytB sequence, and 16–20 microsatellite loci from a total of 524 individuals. Results show that glacial-associated sea-level change limited estuarine habitat to few, widely separated refugia at glacial lowstand, and present-day genetic clades were sourced from specific refugia. Habitat increased during postglacial sea-level rise and refugial populations admixed in newly formed habitats. Continental shelves with active tectonics and/or low sediment supply were steep and hosted fewer, smaller refugia with more genetically differentiated populations than on broader shelves. Approximate Bayesian computation favored the refuge-recolonization scenarios from habitat models over isolation by distance and seaway alternatives, indicating isolation at lowstand is a major diversification mechanism among these estuarine (and perhaps other) coastal species. Because sea-level change is a global phenomenon, we suggest this top-down physical control of extirpation-isolation-recolonization may be an important driver of genetic diversification in coastal taxa inhabiting other topographically complex coasts globally during the Mid- to Late Pleistocene and deeper timescales. This article is protected by copyright. All rights reserved.
... Under scenario 1, the southern and northern populations were modelled as isolated since the LGM and admixed to form the middle group approximately 8 kya. Under scenario 2, the southern population is the only refugium and successively founds the middle and then northern group approximately 8 kya (electronic supplementary material, figure S9, S1, [28]). Posterior values were assessed both directly and logistically per species, and predictive posterior error (PPE) rates were evaluated for each species using all simulations. ...
... Under scenario 1, the southern and northern populations were modelled as isolated since the LGM and admixed to form the middle group approximately 8 kya. Under scenario 2, the southern population is the only refugium and successively founds the middle and then northern group approximately 8 kya (electronic supplementary material, figure S9, S1, [28]). Posterior values were assessed both directly and logistically per species, and predictive posterior error (PPE) rates were evaluated for each species using all simulations. ...
Using a novel combination of palaeohabitat modelling and genetic mixture analyses, we identify and assess a sea-level-driven recolonization process following the Last Glacial Maximum (LGM). Our palaeohabitat modelling reveals dramatic changes in estuarine habitat distribution along the coast of California (USA) and Baja California (Mexico). At the LGM (approx. 20 kya), when sea level was approximately 130 m lower, the palaeo-shoreline was too steep for tidal estuarine habitat formation, eliminating this habitat type from regions where it is currently most abundant, and limiting such estu- aries to a northern and a southern refugium separated by 1000 km. We assess the recolonization of estuaries formed during post-LGM sea-level rise through examination of refugium-associated alleles and approximate Bayesian compu- tation in three species of estuarine fishes. Results reveal sourcing of modern populations from both refugia, which admix in the newly formed habitat between the refuges. We infer a dramatic peak in habitat area between 15 and 10 kya with subsequent decline. Overall, this approach revealed a previously undocumented dynamic and integrated relationship between sea-level change, coastal processes and population genetics. These results extend glacial refugial dynamics to unglaciated subtropical coasts and have significant implications for biotic response to predicted sea-level rise.
We investigate hybridization and introgression between ecologically distinct sister species of silverside fish in the Gulf of California through combined analysis of morphological, sequence, and genotypic data. Water diversions in the past century turned the Colorado River Delta from a normal estuary to a hypersaline inverse estuary, raising concerns for the local fauna, much of which is endangered. Salinity differences are known to generate ecological species pairs and we anticipated that loss of the fresher-water historic salinity regime could alter the adaptive factors maintaining distinction between the broadly distributed Gulf-endemic Colpichthys regis and the narrowly restricted Delta-endemic Colpichthys hubbsi , the species that experienced dramatic environmental change. In this altered environmental context, these long-isolated species (as revealed by Cytochrome b sequences) show genotypic (RAG1, microsatellites) evidence of active hybridization where the species ranges abut, as well as directional introgression from C. regis into the range center of C. hubbsi . Bayesian group assignment (STRUCTURE) on six microsatellite loci and multivariate analyses (DAPC) on both microsatellites and phenotypic data further support substantial recent admixture between the sister species. Although we find no evidence for recent population decline in C. hubbsi based on mitochondrial sequence, introgression may be placing an ancient ecological species at risk of extinction. Such introgressive extinction risk should also pertain to other ecological species historically sustained by the now changing Delta environment. More broadly, salinity gradient associated ecological speciation is evident in silverside species pairs in many estuarine systems around the world. Ecological species pairs among other taxa in such systems are likely poorly understood or cryptic. As water extraction accelerates in river systems worldwide, salinity gradients will necessarily be altered, impacting many more estuary and delta systems. Such alteration of habitats will place biodiversity at risk not only from direct effects of habitat destruction, but also from the potential for the breakdown of ecological species. Thus, evolutionary response to the anthropogenic alteration of salinity gradients in estuaries merits investigation as the number of impacted systems increases around the globe, permitting parallel study of multiple systems, while also permitting a conservation management response to help preserve this little championed component of biodiversity.
