Reproductive isolation in four populations of the striped mouse Rhabdomys
Date
2009-10-15T10:38:26Z
Authors
Stippel, Brian Gareth
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Reproductive isolation was investigated in four phylogenetically and/or
geographically separated populations of Rhabdomys in South Africa. The four populations,
Jonkershoek (Rhabdomys pumilio), Goegap (R. pumilio), Irene (R. dilectus dilectus) and
Suikerbosrand (R. d. chakae), represent the two putative species, R. pumilio (Sparrman,
1784) and R. dilectus De Winton (1897), as well as the two sub-species, R. d. dilectus
(Wroughton, 1905) and R. d. chakae (Wroughton, 1905), of Rhabdomys. The populations
occur > 900 km apart, except for the Irene and Suikerbosrand populations which are
approximately 80 km apart. Inter- and intrapopulation breeding experiments and
behavioural studies were used to test for pre- and/or postzygotic reproductive barriers. In
breeding experiments, most intrapopulation pairs produced offspring. In the interpopulation
breeding tests, except for one litter produced by an Irene-Jonkershoek pair, which did not
survive, only the Jonkershoek-Goegap pairings produced offspring, which were fertile and
had growth rates similar to those of offspring produced in intrapopulation pairings.
However, the smaller litter size of the Jonkershoek-Goegap pairings compared to
intrapopulation pairings, suggests post-zygotic failure between these two R. pumilio
populations. In the behavioural experiments, I tested the responses of females to the soiled
bedding of homotype (same population) and heterotype (different population) males. Two
experiments were conducted: habituation-discrimination and habituation-generalization
tests were used to investigate within- and between-taxon variations in male odour quality and female perception; and choice tests were used to test female preference. The results of
the behavioural experiments indicate that there is variation within the R. pumilio
(Jonkershoek and Goegap) taxon in odour quality, perception and preference. The
Jonkershoek females could discriminate between their own population males and those of
Goegap, and preferred their own males, while the Goegap females were unable to
distinguish between their own population scent and the Jonkershoek population scent and
therefore were unable to display a preference for their own population scent when a
Jonkershoek/Goegap scent choice was presented. The two subspecies of R. dilectus
perceived the scent of males from their own population as being more similar to each other
than to that of R. pumilio, and Irene females perceived the two R. pumilio populations as
different. All four populations displayed assortative mate preference and preferred their own population’s scent over all the others, with the exception of the Goegap population.
My study indicates that phylogeny, and not geography, appears to be a more parsimonious
explanation for the pattern of divergence in these four Rhabdomys populations, although
ecological influences cannot be ruled out.