Population genetics of seaside Sparrow (Ammodramus maritimus) subspecies along the gulf of Mexico.

Stefan Woltmann,Philip C Stouffer,Christine M Bergeon Burns,Sabrina S Taylor,Mollie F Cashner,Mark S Woodrey,Genlou Sun

doi:10.1371/journal.pone.0112739

Abstract

Seaside Sparrows (Ammodramus maritimus) along the Gulf of Mexico are currently recognized as four subspecies, including taxa in Florida (A. m. juncicola and A. m. peninsulae) and southern Texas (Ammodramus m. sennetti), plus a widespread taxon between them (A. m. fisheri). We examined population genetic structure of this “Gulf Coast” clade using microsatellite and mtDNA data. Results of Bayesian analyses (Structure, GeneLand) of microsatellite data from nine locations do not entirely align with current subspecific taxonomy. Ammodramus m. sennetti from southern Texas is significantly differentiated from all other populations, but we found evidence of an admixture zone with A. m. fisheri near Corpus Christi. The two subspecies along the northern Gulf Coast of Florida are significantly differentiated from both A. m. sennetti and A. m. fisheri, but are not distinct from each other. We found a weak signal of isolation by distance within A. m. fisheri, indicating this population is not entirely panmictic throughout its range. Although continued conservation concern is warranted for all populations along the Gulf Coast, A. m. fisheri appears to be more secure than the far smaller populations in south Texas and the northern Florida Gulf Coast. In particular, the most genetically distinct populations, those in Texas south of Corpus Christi, occupy unique habitats within a very small geographic range.

Highlights

Isolated populations of organisms inhabiting patchily distributed habitat often form genetically or morphologically distinct populations that may be recognized as species or subspecies [1,2,3]
A majority of pairwise FST values were statistically significant (P,0.001); both FST and Dest were consistently higher in all comparisons involving location 1, and lowest within samples encompassing A. m. fisheri (Table 4)
Our microsatellite data are consistent with the recognition of three populations: A. m. cf. sennetti, A. m. fisheri, and a combined group including A. m. juncicola and A. m. peninsuale

Summary

Introduction

Isolated populations of organisms inhabiting patchily distributed habitat often form genetically or morphologically distinct populations that may be recognized as species or subspecies [1,2,3]. From a conservation standpoint, protecting multiple small populations is important to preserving genetic diversity, but can be difficult in practice [4]. The use of subspecies to identify ecologically or morphologically distinct populations has a long history in ornithology [3,5], but issues regarding diagnostic criteria and the role of subspecies in conservation are continually debated and refined (e.g., [6,7]). In the United States, the Endangered Species Act (ESA) considers ‘‘distinct population segments’’ as potentially eligible for special protections. It is important to understand whether taxonomically recognized subspecies can reasonably be considered distinct population segments with unique genetic or ecological characteristics [3]

Methods

Results

Discussion

Conclusion