Phylogeography of Supralittoral Rocky Intertidal Ligia Isopods in the Pacific Region from Central California to Central Mexico

Abstract

Background Ligia isopods are widely distributed in the Pacific rocky intertidal shores from central California to central Mexico, including the Gulf of California. Yet, their biological characteristics restrict them to complete their life cycles in a very narrow range of the rocky intertidal supralittoral. Herein, we examine phylogeographic patterns of Ligia isopods from 122 localities between central California and central Mexico. We expect to find high levels of allopatric diversity. In addition, we expect the phylogeographic patterns to show signatures of past vicariant events that occurred in this geologically dynamic region.Methodology/Principal FindingsWe sequenced two mitochondrial genes (Cytochrome Oxidase I and 16S ribosomal DNA). We conducted Maximum Likelihood and Bayesian phylogenetic analyses. We found many divergent clades that, in general, group according to geography. Some of the most striking features of the Ligia phylogeographic pattern include: (1) deep mid-peninsular phylogeographic breaks on the Pacific and Gulf sides of Baja peninsula; (2) within the Gulf lineages, the northern peninsula is most closely related to the northern mainland, while the southern peninsula is most closely related to the central-southern mainland; and, (3) the southernmost portion of the peninsula (Cape Region) is most closely related to the southernmost portion of mainland.Conclusions/SignificanceOur results shed light on the phylogenetic relationships of Ligia populations in the study area. This study probably represents the finest-scale phylogeographic examination for any organism to date in this region. Presence of highly divergent lineages suggests multiple Ligia species exist in this region. The phylogeographic patterns of Ligia in the Gulf of California and Baja peninsula are incongruent with a widely accepted vicariant scenario among phylogeographers, but consistent with aspects of alternative geological hypotheses and phylo- and biogeographic patterns of several other taxa. Our findings contribute to the ongoing debate regarding the geological origin of this important biogeographic region.

Phylogeography of Semiterrestrial Isopod,Tylos granuliferus, on East Asian Coasts

“…However, several semiterrestrial coastal species do not show clear relationships between their distributions and local ocean currents (e.g., coastal tiger beetles: Satoh et al, 2004, Ligia spp. : Itani, 2000Hurtado et al, 2010).…”

“…Phylogenetic analyses of mitochondrial DNA data have revealed that some semiterrestrial coastal isopods display noncurrent-related and complex distribution patterns in several areas (Ligia spp. : Itani, 2000;Hurtado et al, 2010).…”

Isopods of the genus Ligia as potential biomonitors of trace metals from the gulf of California and pacific coast of the Baja California peninsula.

“…First, they are widely distributed along the coast of the Gulf of California, its islands, and the Pacific coast of the Baja California peninsula. Hurtado et al (2010) report the presence of these isopods in 4100 coastal localities in this region, which are subject to varying levels of anthropogenic activity, and they are likely to be found at many yet unexplored localities. Second, they occur exclusively at beaches with rocky supralittoral zones, where they are restricted to the narrow range between the splash zone and the supralittoral.…”

Pollution of radiocesium and radiosilver in wharf roach (Ligia sp.) by the Fukushima Dai-ichi Nuclear Power Plant accident

“…The wharf roach (Ligia sp., Crustacea, Isopoda, Ligiidae) is a cosmopolitan semi-terrestrial crustacean distributed in temperate and tropical areas [8][9][10]. Abundant wharf roaches can be found on the seashore among pilings, beach fortifications, jetties, and rocks in most estuary and coastal areas of Japan [11,12].…”

“…Abundant wharf roaches can be found on the seashore among pilings, beach fortifications, jetties, and rocks in most estuary and coastal areas of Japan [11,12]. Owing to some of their ecophysiological characteristics, these crustaceans are highly constrained throughout their life cycle to remain on the same beach [10], and thus may serve as a good bioindicator of radioactive contamination of their habitats [13].…”