Contrasting Phylogeography of Sandy vs. Rocky Supralittoral Isopods in the Megadiverse and Geologically Dynamic Gulf of California and Adjacent Areas

Abstract

Phylogeographic studies of animals with low vagility and restricted to patchy habitats of the supralittoral zone, can uncover unknown diversity and shed light on processes that shaped evolution along a continent’s edge. The Pacific coast between southern California and central Mexico, including the megadiverse Gulf of California, offers a remarkable setting to study biological diversification in the supralittoral. A complex geological history coupled with cyclical fluctuations in temperature and sea level provided ample opportunities for diversification of supralittoral organisms. Indeed, a previous phylogeographic study of Ligia, a supralittoral isopod that has limited dispersal abilities and is restricted to rocky patches, revealed high levels of morphologically cryptic diversity. Herein, we examined phylogeographic patterns of Tylos, another supralittoral isopod with limited dispersal potential, but whose habitat (i.e., sandy shores) appears to be more extensive and connected than that of Ligia. We conducted Maximum Likelihood and Bayesian phylogenetic analyses on mitochondrial and nuclear DNA sequences. These analyses revealed multiple highly divergent lineages with discrete regional distributions, despite the recognition of a single valid species for this region. A traditional species-diagnostic morphological trait distinguished several of these lineages. The phylogeographic patterns of Tylos inside the Gulf of California show a deep and complex history. In contrast, patterns along the Pacific region between southern California and the Baja Peninsula indicate a recent range expansion, probably postglacial and related to changes in sea surface temperature (SST). In general, the phylogeographic patterns of Tylos differed from those of Ligia. Differences in the extension and connectivity of the habitats occupied by Tylos and Ligia may account for the different degrees of population isolation experienced by these two isopods and their contrasting phylogeographic patterns. Identification of divergent lineages of Tylos in the study area is important for conservation, as some populations are threatened by human activities.

Multiple transisthmian divergences, extensive cryptic diversity, occasional long‐distance dispersal, and biogeographic patterns in a marine coastal isopod with an amphi‐American distribution

“…This is in contrast to what has been found for supralittoral isopods of the genus Tylos , for which colonization of the northeastern Pacific appears to have proceeded from the Caribbean (Hurtado et al. , ). Paleontological studies of the Gulf of California report that most fauna‐rich sediments found in this region have affinities with Caribbean fauna (Escalona‐Alcázar et al.…”

“…Third, we also examined whether populations of this isopod in the Gulf of California have closer affinities with lineages from the Caribbean, as has been observed for other coastal isopods (Hurtado et al. , ) and for marine fossils (Smith ; Escalona‐Alcázar et al. ).…”

“…Concordantly, recent phylogeographic studies of intertidal isopods indicate that several species presumed to occupy broad distributions, instead correspond to diverse species complexes comprised of multiple highly divergent cryptic lineages, which often have very restricted geographic ranges (Sponer and Lessios ; Hurtado et al. , , ; Varela and Haye ; Santamaria et al. , , ).…”

Global Diversification at the Harsh Sea-Land Interface: Mitochondrial Phylogeny of the Supralittoral Isopod Genus Tylos (Tylidae, Oniscidea)

“…Juveniles of some species, however, may be able to surf by rolling themselves into a ball, potentially facilitating dispersal among nearby beaches [7], [15]. Consistent with their biological characteristics, high levels of population genetic differentiation have been observed at small geographic scales in members of Tylos , implying that surrounding unsuitable habitats constitute effective dispersal barriers and that the potential for population isolation is high [9]. Furthermore, factors that can dramatically modify the distribution of coastline habitats, such as tectonic activity and eustatic sea level fluctuations, as well as climate change, appear to strongly influence the evolutionary histories of these isopods [9].…”

Endemism and evolution in the littoral woodlouse Halophiloscia Verhoeff, 1908 (Crustacea, Isopoda, Oniscidea) from the Canary Islands: implications for conservation policies

“…Traditionally, littoral isopod species have been considered as good disperses (Vandel, ). Nevertheless, recent phylogeographic studies on the supralittoral isopod genera Tylos Audouin, 1826 and Ligia Fabricius, 1798, have revealed highly structured populations and deep divergences among multiple regional lineages (Hurtado et al ., , ; Markow & Pfeiler, ; Eberl et al ., ). Our results support in part this latter observation.…”