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Sci Rep
2020 Mar 05;101:4130. doi: 10.1038/s41598-020-61168-y.
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Relative tail length correlates with body condition in male but not in female crowned leafnose snakes (Lytorhynchus diadema).
Sivan J
,
Hadad S
,
Tesler I
,
Rosenstrauch A
,
Allan Degen A
,
Kam M
.
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Reproductive success is the ultimate measure of individual quality; however, it is difficult to determine in free-living animals. Therefore, indirect measures that are related to reproduction are generally employed. In snakes, males typically possess longer tails than females and this sexual size dimorphism in tail length (TL) has generally been attributed to the importance of the tail in mating and reproduction. Thus, intra-sexual differences in tail length, specifically within males, were hypothesized to reflect individual quality. We used a body condition index (BCI) as a measure of quality in snakes and predicted that tail length would be correlated with BCI in males. We tested our prediction by determining BCI in the free-ranging adult male and female crowned leafnose snake (Lytorhynchus diadema), a colubrid species that inhabits mainly desert sand dunes. The relative TL was correlated positively and significantly to BCI in males (F1,131 = 11.05; r2adj = 0.07; P < 0.01) but not in females, thus supporting our prediction. This is the first time that the relationship between TL and body condition was tested in a free-ranging species. In addition, sexual size dimorphism of TL increased intra-specifically with body size, which was also found in interspecific analyses following Rensch''s rule.
Figure 1. A Lytorhynchus diadema at our research site in the Negev Desert.
Figure 2. The effect of snout-vent length (SVL) on tail length in male (triangles; dashed line) and female (circles; solid line) Lytorhynchus diadema. The gap between the two regression lines represents the significant increase in sexual dimorphism of tail length with SVL; increase rate of tail length with SVL is higher in males than females (see text for explanation).
Figure 3. The effect of the residuals of tail length (TLr) on body condition index (BCI) in male (triangles; dashed line; the regression equation took the form of BCI = 1.01 TLr + 11.73; r2 = 0.07; P < 0.01; n = 133) and female (circles and solid line at mean BCI because of non-significant relationship; P = 0.17; n = 107) free-ranging Lytorhynchus diadema (see text for explanation).
Figure 4. Three Lytorhynchus diadema males (M1, M2, M3) coiled around a female (F) at the entrance of a rodent burrow in a ‘mating ball’. L. diadema vary in color allowing the distinction among individuals.
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