Abstract
Genetic monogamy is the rule for many species of seahorse, including the West Australian seahorse Hippocampus subelongatus. In this paper, we revisit mark-recapture and genetic data of H. subelongatus, allowing a detailed characterization of movement distances, home range sizes and home range overlaps for each individual of known sex, paired status (paired or unpaired) and body size. As predicted, we find that females have larger home ranges and move greater distances compared to males. We also confirm our prediction that the home ranges of pair-bonded individuals (members of a pair known to reproduce together) overlap more on average than home ranges of randomly chosen individuals of the opposite or same sex. Both sexes, regardless of paired status, had home ranges that overlapped with, on average, 6–10 opposite-sex individuals. The average overlap area among female home ranges was significantly larger than the overlap among male home ranges, probably reflecting females having larger home ranges combined with a female biased adult sex ratio. Despite a prediction that unpaired individuals would need to move around to find a mate, we find no evidence that unpaired members of either sex moved more than paired individuals of the same sex. We also find no effect of body size on home range size, distance moved or number of other individuals with which a home range overlapped. These patterns of movement and overlap in home ranges among individuals of both sexes suggest that low mate availability is not a likely explanation for the maintenance of monogamy in the West Australian seahorse.
Highlights
Space use is often related to an animal’s mating system (Emlen and Oring 1977; Hixon 1987; Clutton-Brock 1989)
We have shown that female H. subelongatus had larger home range areas and moved greater distances than males and that the home ranges of mated pairs overlapped more with each other than with any randomly chosen individual of the opposite sex
Our results suggest that home range use in H. subelongatus is mainly affected by sex and by the partner’s home range
Summary
Space use is often related to an animal’s mating system (Emlen and Oring 1977; Hixon 1987; Clutton-Brock 1989). Sex differences in movement patterns can arise from ecological differences between the sexes or from differing reproductive interests. The relationship between mating systems and space use is especially interesting, as the causal arrow can point either direction. Males of a polygynous species might be motivated to move large distances to find additional suitable mates, resulting in greater space use by males (Brown and Weatherhead 1999; Radespiel 2000). Males with large home ranges for feeding purposes or other ecological reasons could be polygynous merely because their territories overlap with the home ranges of multiple females (Hixon 1987)
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