Concordant results

Inferences of sex-biased dispsersal have been made in a wide range of taxa using all four genetic methods outlined above (Table 6.6). Because no method is infallible, conclusions may be more robust if multiple methods have provided concordant results. This was the case in a study of two hyrax species, the bush hyrax (Heterohyrax brucei) and the rock hyrax (Procavia johnstoni), in the Serengeti National Park. Both species live within a classic metapopulation structure characterized by distinct habitat patches consisting of rock outcrops that are separated by wide expanses of grass plains. Local populations are subject to extinction--recolonization events, and dispersal between populations is ongoing.

A recent genetic study generated several lines of evidence that all revealed female-biased dispersal in the bush hyrax, and equal dispersal in male and female rock hyrax. Part of this evidence came from microsatellite-based FST values, which were higher in males than females in the bush hyrax but comparable in both sexes in the rock hyrax. In addition, assignment tests identified a greater proportion of immigrant females than immigrant males in the bush hyrax but not in the rock hyrax (Figure 6.12), and relatedness among females within sites was relatively high in the rock hyrax but not in the bush hyrax. These results were somewhat surprising, because earlier mark--recapture studies had concluded that dispersal in both species was male-biased. This discrepancy may be explained if

Table 6.6 Examples of sex-biased dispersal in a variety of taxa. Note that although examples of female-biased dispersal in mammals and male-biased dispersal in birds are exceptions to the rule, some have been included here to show that they can occur

Dispersing Method Species sex of analysis3 Reference

Mammals

Eastern grey kangaroo

Male

MI

Zenger, Eldridge and

(Macropus giganteus)

Cooper (2003)

Bechstein's bat

Male

MI

Kerth, Nayer and Petit

(Myotis bechsteinii)

(2002a); Kerth, Safi

and Konig (2002b)

Dall's porpoise

Male

MI

Escorza-Trevino and

(Phocoenoides dalli)

Dizon (2000)

Wolverine (Gulo gulo)

Male

GD,

A

Cegelski, Waits and

Anderson (2003)

Greater white-toothed

Female

GD

Favre et al. (1997)

shrew (Crocidura russula)

Yellow-spotted rock

Female

GD,

A, R

Gerlach and Hoeck (2001)

hyrax ( Heterohyrax

brucei)

River otter (Lontra

Male

GD

Blundell et al. (2002)

canadensis)

Birds

Great reed warbler

Female

A

Hansson, Bensch and

(Acrocephalus arundinaceus)

Hasselquist (2003)

Red grouse (Lagopus

Female

MI

Piertney et al. (2000)

lagopus scoticus)

Yellow warbler

Male

MI

Gibbs, Dawson and

(Dendroica petechia)

Hobson (2000)

Red-billed quelea

Male

A

Dallimer et al. (2002)

(Quelea quelea)

Fish

Brown trout (Salmo trutta)

Male

A

Bekkevold, Hansen and

Mensberg (2004)

Lake Malawi cichlids

Male

R

Knight et al. (1999)

(Pseudotropheus zebra

and P. callainos)

Lake Tanganyika cichlid

Female

R

Taylor et al. (2003)

(Eretmodus cyanostictus)

Reptiles

Australian lizard

Male

R

Gardner et al. (2001)

(Egernia stokesii)

Marine iguana

Male

GD,

MI

Rassmann et al. (1997)

(Amblyrhynchus cristatus)

(Amblyrhynchus cristatus)

Table 6.6 (Continued)

Amphibians

Bullfrog (Rana catesbeiana) Female Tungara frog (Physalaemus Male pustulosus)

Invertebrates

Tick (Ixodes ricinus) Ponerine ant (Diacamma cyaneiventre) Narrow headed ant (Formica exsecta)

Male Male

Male

R MI

de Meeus et al. (2002) Douhms, Cabrera and

Sundstrom, Keller and

Peeters (2002)

Chapuisat (2003)

aA, assignment tests; GD, genetic differentiation in males and females based on data from the same loci; R, relatedness; MI, marker inheritance, which refers to genetic differentiation based on biparentally versus uniparentally inherited markers.

Figure 6.12 Male and female dispersal in bush and rock hyraxes on the Serengeti, as revealed by assignment tests. The bush hyrax shows evidence of female-biased dispersal, whereas dispersal of males and females in the rock hyrax is comparable. Data from Gerlach and Hoeck (2001)

bush hyrax males disperse more often than females but either die en route or are less successful than females at reproducing in their new populations, in which case male dispersal would not equate with male-mediated gene flow (Gerlach and Hoeck, 2001).

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