Bacular variation and allometry in the western martenMartes caurina |
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Authors: | Edward H Miller David W Nagorsen |
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Institution: | (1) Mammalian Behaviour and Evolution Group, Department of Veterinary Preclinical Science, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK |
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Abstract: | Many sexually-selected structures are variable and positively allometric relative to body size. For the western martenMartes caurina Merriam, 1890 from Vancouver Island, British Columbia, we investigated variation in the baculum compared with other bones
and allometry of bacular to body size. Carcass length did not differ, and humeral and mandibular lengths differed little (<
1 and 2%, respectively), between age groupings < 1 and ≥ 1 yr old. In contrast, bacular length increased by 16%, and thickness
by 29% (mid shaft) and 86% (basal) between those groupings, and thickness and mass continued to grow after the second year
of life. Controlling for body size, bacular size varied more than humeral or mandibular size (CV for linear variables ∼4–8%
for baculum, ∼2% for humerus or mandible). Some positive static allometry of bacular size to body size was found, but correlations
between bacular and body size were weak (r=0.3–0.4). So penile size as related to bacular size could be a reliable but imprecise quality indicator during copulation.
Weak polygamy (serial promiscuity), complex copulatory mechanisms, and high energetic costs of reproduction, likely select
for multiple cues in mate-choice by females, not just penile cues affected by bacular size or shape. |
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