Population Genetics of Seaside Sparrow (Ammodramus maritimus) Subspecies along the Gulf of Mexico

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.

Genome-wide assessment of population structure in Florida’s coastal seaside sparrows

“…MRK, HIC, ADM) were genetically indistinguishable from A. m peninsulae, and other birds in Florida's panhandle from Pensacola Bay east to St. Vincent NWR (GAR, HOG, VIN) were indistinguishable from birds captured in Mississippi (SS), which are considered A. m. fisheri. These findings reinforce conclusions from previous studies using mitochondrial DNA and microsatellites and help to clarify the genetic identity of the seaside sparrow populations in the western panhandle (Avise and Nelson 1989;Woltmann et al 2014).…”

“…We used samples from Georgia, Northeast Florida, and Mississippi to assess the genetic relationships of A. m. peninsulae and A. m. juncicola with other Florida subspecies. Thirteen of the Florida sites were sampled during 2016-2018, 25 samples from Georgia were collected in 2016 (USFWS 2018), 20 samples from Mississippi were collected in 2012 (Woltmann et al, 2014), and 37 samples from a 14th Florida site were collected in 2001 (Hill and Post 2005). Biologists with the FWC captured 292 seaside sparrows using mistnets during 2016-2018.…”

“…Taxonomy of the seaside sparrow has had a complicated history with some subspecies previously deemed to be separate species (Austin 1983;McDonald 1988;Rising 2005;Robbins 1983;Woltmann et al 2014;AOU 1957AOU , 1973. Many current divisions are based on slight phenotypic differences and geographic distributions (FWC 2013;McDonald 1988).…”

“…The ranges of A. m. juncicola and A. m. peninsulae remain uncertain (FWC 2013;Woltmann et al 2014). There are differing accounts of where A. m. juncicola and A. m. peninsulae are found and there is confusion about the identity of seaside sparrow populations in Florida's western panhandle (McDonald 1988;Post and Greenlaw 2018;Woltmann et al 2014). For example, Quay and Funderburg (1983) proposed a much narrower range for A.m. juncicola in Florida's Big Bend region (i.e.…”

“…A genetic study conducted by Avise and Nelson (1989) revealed significant differences between Atlantic and Gulf coast populations, but the genetic relationships among Florida's Gulf coast populations, particularly those between A.m. juncicola and A. m. peninsulae, are not as clear (Avise and Nelson 1989;McDonald 1988;Woltmann et al 2014). Although a more recent study utilizing mtDNA and microsatellite markers found no significant differences among Florida's Gulf coast populations, Woltmann et al (2014) stated that greater sample sizes and genome-wide sampling would be necessary to distinguish whether the two subspecies were genetically distinct (Woltmann et al 2014). In addition, their samples were collected in winter, and non-breeding individuals may have been in the areas they sampled.…”