Tempo and mode of speciation in the Baja California disjunct fish species Anisotremus davidsonii

Abstract

The Baja California region provides a natural setting for studying the early mechanisms of allopatric speciation in marine systems. Disjunct fish populations from several species that occur in the northern Gulf of California and northern Pacific coast of Baja California, but are absent from its southern shores, were previously shown to be genetically isolated, making them excellent candidates for studying allopatry. In addition, one of these species, the sargo Anisotremus davidsonii, has two pairs of congeneric Panamic trans-isthmian geminate species that allow for internal molecular clock calibration. Phylogeographic and demographic approaches based on mitochondrial (cytochrome b) and nuclear (S7 ribosomal protein) sequences showed that A. davidsonii entered the gulf from the south, and later colonized the Pacific coast, approximately 0.6-0.16 million years ago. Pacific coast colonization may have used a route either around the southern cape of Baja California or across the peninsula through a natural seaway. However, while several seaways have been described from different geological times, none matches the dates of population disjunction, yet much geological work remains to be done in that area. At the present time, there is no evidence for dispersal around the southern tip of the Baja California Peninsula. Signatures of incipient allopatric speciation were observed, such as the reciprocal monophyly of disjunct populations for the mitochondrial marker. However, other characteristics were lacking, such as a strong difference in divergence and coalescence times. Taken together, these results suggest that disjunct populations of A. davidsonii may be consistent with the earliest stages of allopatric speciation.

Atlantic reef fish biogeography and evolution

“…The following phylogenies were used for analysis and inferences: Abudefduf (Quenouille et al, 2004), Acanthostracion/ Lactophrys (Klassen, 1995), Acanthurus (Rocha et al, 2002), Alphestes (Craig et al, 2004(Craig et al, , 2006, Anisotremus (Bernard! & Lape, 2005), Aulostomus , Centropyge 'xiphipops' complex (Bowen et al, 2006a), chaenopsids (Hastings, 2000), Chromis (Quenouille et al, 2004 (Heiser et al, 2000), Dermatolepis (Craig et al, 2004), Diplodus (Summerer et al, 2001), Elacatinus (Taylor & Hellberg, 2005), Gnatholepis (Rocha et al, 2005a), Gobiesocinae (Briggs, 1955), Hippocampus (Casey et al, 2004), Halichoeres (Rocha, 2004;Barber & Bellwood, 2005), Holacanthus (Bellwood et al, 2004;G.…”

Phylogeography of the shanny Lipophrys pholis (Pisces: Blenniidae) in the NE Atlantic records signs of major expansion event older than the last glaciation

“…In order to compute estimates of effective population size, their changes with time, and the age of populations, we used two divergence rates for CR: 10% (Bowen et al, 2006 between Centropyge lineages) and 3.6% (Domingues et al, 2005 for the sister species Chromis chromis and C. limbata) and one for S7: 0.46% (Bernardi and Lape, 2005 for Anisotremus taeniatus and A. verginicus, two transisthmian sister species of blennids separated 6.0-5.3 Mya before the closure of the isthmus of Panama). Values are divergence rates per million years and were halved to get an estimate of mutation rates per lineage per million years.…”

Post-glacial habitat release and incipient speciation in the genus Delphinus

“…In the relatively homogeneous marine environment, cryptic diversity among populations or incipient species has been described for a range of taxa from sessile invertebrates (Landry et al, 2003) to fish (Bernardi and Lape, 2005) and marine mammals (Moura et al, 2013). Resource specializations promote intraspecific differential niche use and may lead to genetic structure if gene flow is also restricted, for example, through assortative mating, physical separation within local environments or by divergent selection (Rundle and Nosil, 2005;Nosil, 2012).…”