Genetic analyses of historic and modern marbled murrelets suggest decoupling of migration and gene flow after habitat fragmentation

Abstract

The dispersal of individuals among fragmented populations is generally thought to prevent genetic and demographic isolation, and ultimately reduce extinction risk. In this study, we show that a century of reduction in coastal old-growth forests, as well as a number of other environmental factors, has probably resulted in the genetic divergence of marbled murrelets (Brachyramphus marmoratus) in central California, despite the fact that 7 per cent of modern-sampled murrelets in this population were classified as migrants using genetic assignment tests. Genetic differentiation appears to persist because individuals dispersing from northern populations contributed relatively few young to the central California population, as indicated by the fact that migrants were much less likely to be members of parent-offspring pairs than residents (10.5% versus 45.4%). Moreover, a recent 1.4 per cent annual increase in the proportion of migrants in central California, without appreciable reproduction, may have masked an underlying decline in the resident population without resulting in demographic rescue. Our results emphasize the need to understand the behaviour of migrants and the extent to which they contribute offspring in order to determine whether dispersal results in gene flow and prevents declines in resident populations.

The value of space‐for‐time substitution for studying fine‐scale microevolutionary processes

“…Several carefully designed studies (Peery et al 2010, Ugelvig et al 2011, Martin et al 2014) detected patterns of IBT that were roughly linear, as expected. Moreover, these studies also suggest that rates of genetic differentiation through time and space are comparable over relatively fine spatial and temporal scales, which is particularly important for studies of microevolutionary processes acting at finer scales and over smaller spatiotemporal domains.…”

“…For example, Peery et al (2010Peery et al ( ) evaluated historic (1888Peery et al ( -1940Peery et al ( ) and modern (1997Peery et al ( -2007 samples of marbled murrelets Brachyramphus marmoratus and characterized both spatial F ST and temporal F ST for historic and modern samples. They found increased levels of differentiation in central Californian populations through time (IBT) and suggest that small population size and, therefore, genetic drift drove the differentiation, consistent with expectations.…”

Characterizing dispersal patterns in a threatened seabird with limited genetic structure

“…When simulating genotypes, we assumed that microsatellites evolved according to a stepwise mutation model and mutated at a rate of 10 −5 mutations per locus per generation. Also, we assumed that, 12 generations in the past (approximately 100 years, assuming a generation time of 8 years for marbled murrelets; Peery et al. 2010), a small population of N e = 100, representing central California, split from a much larger historic and equilibrium population of N e = 367 500, representing the northern populations, and that the two populations were unconnected by gene flow ( m = 0) following the split.…”

Use of molecular genetics for understanding seabird evolution, ecology and conservation

“…1; e.g. Peery et al 2010, Hailer et al 2011). For example, Techow et al (2010) used cyto chrome b and 6 microsatellite loci to examine the phylogeography and speciation history of giant petrels Macronectes spp.…”