Mechanisms of Population Differentiation in Marbled Murrelets: Historical Versus Contemporary Processes

Abstract

.— Mechanisms of population differentiation in highly vagile species such as seabirds are poorly understood. Previous studies of marbled murrelets (Brachyramphus marmoratus; Charadriiformes: Alcidae) found significant population genetic structure, but could not determine whether this structure is due to historical vicariance (e.g., due to Pleistocene glaciers), isolation by distance, drift or selection in peripheral populations, or nesting habitat selection. To discriminate among these possibilities, we analyzed sequence variation in nine nuclear introns from 120 marbled murrelets sampled from British Columbia to the western Aleutian Islands. Mismatch distributions indicated that murrelets underwent at least one population expansion during the Pleistocene and probably are not in genetic equilibrium. Maximum‐likelihood analysis of allele frequencies suggested that murrelets from “mainland” sites (from the Alaskan Peninsula east) are genetically different from those in the Aleutians and that these two lineages diverged prior to the last glaciation. Analyses of molecular variance, as well as estimates of gene flow derived using coalescent theory, indicate that population genetic structure is best explained by peripheral isolation of murrelets in the Aleutian Islands, rather than by selection associated with different nesting habitats. No isolation‐by‐distance effects could be detected. Our results are consistent with a rapid expansion of murrelets from a single refugium during the early–mid Pleistocene, subsequent isolation and divergence in two or more refugia during the final Pleistocene glacial advance, and secondary contact following retreat of the ice sheets. Population genetic structure now appears to be maintained by distance effects combined with small populations and a highly fragmented habitat in the Aleutian Islands.

Biological Impacts of Climatic Change on a Beringian Endemic: Cryptic Refugia in the Establishment and Differentiation of the Rock Sandpiper (Calidris Ptilocnemis)

“…Contemporary gene flow is suggested. Additional support for these two locations as refugia comes from other studies that have shown that one or both of these locations were refugia for other bird species (Holder et al, 1999;Congdon et al, 2000).…”

“…There is evidence that at least one large glacial refugium was present in Beringia in the areas north of the ice in the Bering land bridge area and in present-day Alaska and Siberia (Pielou, 1991; Figure 1). Researchers studying the phylogeography (geographic distributions of genetic lineages; Avise, 2000) of two bird species, the rock ptarmigan (Lagopus mutus; Holder et al, 1999) and the marbled murrelet (Brachyramphus marmoratus; Congdon et al, 2000), have postulated that one or two previously unknown refugia were present in the Bering Sea region, likely in the Aleutian Islands. However, there is presently no geological or fossil evidence to corroborate these cryptic Bering Sea refugia.…”

Population Genetic Structure and Conservation of the Galápagos Petrel (Pterodroma phaeopygia)

“…Beerli 1999;Hedrick 1999), some of which may not hold for petrels (e.g. Congdon et al 2000). In contrast, molecular assignments using programs such as BAYESASS make few assumptions (reviewed in Manel et al 2005).…”

Limited genetic differentiation among breeding, molting, and wintering groups of the threatened Steller’s eider: the role of historic and contemporary factors

“…Defining such units relies upon a wide array of criteria and for migratory birds may include morphological or plumage characteristics, behavioral patterns quantified by banding or radio telemetry, or geographic separation of population segments during all or part of the annual cycle. Genetic markers are now widely used to quantify population divergence, identify or clarify management and taxonomic units, and offer insights into both historical and more contemporary processes involved in levels of divergence (e.g., Congdon et al 2000;Scribner et al 2003;Spruell et al 2003;Gay et al 2004). Yet for many migratory species, historical processes (e.g., Pleistocene ice movements) have substantially influenced gene flow and contemporary geographic distribution (Hewitt 2000), resulting in disparities between behavioral patterns, such as site fidelity or philopatry, and range-wide genetic characteristics.…”