Genetic consequences of population subdivision: the marsupial Micoureus paraguayanus (Mammalia: Didelphimorphia) as a case study

Abstract

ABSTRACT. Habitat fragmentation may cause population subdivision, affecting genetic variation, leading to heterozygosity loss and increased inbreeding, and contributing to population extinction. However, some genetic models have shown that under some conditions, population subdivision can favor heterozygosity and allelic diversity, and small populations may adapt to inbreeding. Here I investigate the relationship between population subdivision and genetic diversity for the marsupial Micoureus paraguayanus (Tate, 1931) using the program Vortex. Hypothetical populations of 100 and 2000 individuals were partitioned into 1, 2, 5 or 10 populations that were linked by varying rates of dispersal and also by sex-biased dispersal. Results suggested that heterozygosity and allelic diversity declined rapidly when a population was subdivided. Genetic and demographic stochasticity diminished the effectiveness of selection against recessive lethal alleles. Dispersal partly reversed the impacts of population subdivision. However, even high rates of dispersal did not eliminate demographic fluctuations or prevent extinction. Although gene flow largely prevented genetic divergence between populations, dispersal did not prevent heterozygosity from being lost more rapidly in subdivided populations than in single populations of equivalent total size. The dynamics of small, fragmented populations were critically dependent on interactions between demographic and genetic processes. Populations of M. paraguayanus may have to be relatively large and continuous to avoid significant losses of genetic diversity.

Genetic introgression and the survival of Florida panther kittens

“…The population ecology and population genetics of a species are frequently not integrated in these models. When they are, the demographic effects of inbreeding are often based on data from captive animals and/or program defaults (e.g., Brito 2009; Maehr et al 2002; Nilsson 2004). An important first step towards developing integrated models is determining the functional relationship between measures of inbreeding and juvenile survival in the wild, especially for managed populations.…”

The Impacts of Population Subdivision on the Viability of Brachyteles hypoxanthus

“…PVA models based on empirical data also showed the same trend for some mammals Lindenmayer and Lacy, 1995a;Brito and Fonseca, 2007;Brito, 2009a]. In a metapopulation structure, the size of the constituent populations seems to be an important factor for long-term persistence [Fahrig, 1997[Fahrig, , 1998[Fahrig, , 2001Hanski and Gaggiotti, 2004].…”

“…Enhancing connectivity through dispersal had the result of further increasing population instability through metapopulation stochasticity [Lindenmayer and Lacy, 1995a, b;Brito and Fonseca, 2007;Brito, 2009a]. Dispersal among populations may also generate synchronous population dynamics, where temporal fluctuations in population size coincide (e.g.…”