Reproductive ecology of female Mexican lance‐headed rattlesnakes

Abstract

Our understanding of snake biology is heavily biased towards species and populations occurring at higher latitudes. In particular, little information is available concerning the biology of the numerous species of Mexican rattlesnakes. We studied the reproductive ecology of female Mexican lance-headed rattlesnakes Crotalus polystictus in a montane (c. 2500 m a.s.l.) valley of the Rio Lerma, in the Mexican state of Me´xico. We collected data from 162 different females and 203 litters over 4 years (2004)(2005)(2006)(2007). Parturition coincided with summer monsoon rains, with the majority of females giving birth in late June and early July. Larger females and females gestating larger litters typically gave birth earlier in the summer than did smaller females and females gestating smaller litters. Some females matured rapidly; 26 females reproduced as 3-year olds, 17 as 2-year olds and a single female reproduced at 1 year of age. Females commonly reproduced in consecutive years. Litter size and mean neonate size increased with maternal body length; however, the relative clutch mass did not vary with female size. The mean litter size was 7.3 neonates (range 3-15), and the mean neonate body length (snout-vent length) and mass were 198 mm and 8.7 g. Neonate size varied less than did other litter characteristics. Rapid maturity, frequent reproduction and synchronization of parturition with seasonal precipitation are consistent with previously observed patterns of snake reproduction at lower latitudes.

Female Reproduction inThamnophis scaliger: The Significance of Parturition Timing

“…By contrast, mean neonate body size (mass) was not affected by female size or by litter size in T. scaliger. These findings would indicate that offspring size is fixed in this species, suggesting selection on neonate size that will produce the highest fitness for the species, as already reported in other snake species (Ford and Seigel, 1994;Charnov, 2002;Setser et al, 2010; but see Kissner and Weatherhead, 2005).…”

“…This synchrony between reproduction timing and certain environmental conditions has been reported for the syntopic Crotalus polystictus (Setser et al, 2010), and it is a common trend in most tropical and subtropical snakes (Mathies, 2011). Synchronized reproduction with particular abiotic and biotic factors may maximize reproductive success, benefiting both gestating females and neonates (Shine, 2003).…”

“…In snakes, fat stores (i.e., endogenous energy) constitute one of the thresholds that affect this decision Santos and Llorente, 2004). Although adult females of live-bearing snakes may reproduce in sequential years in some natural populations (Setser et al, 2010), reproductive rates of these snakes tend to be much lower than those of oviparous species (Shine and Brown, 2008). Viviparous snakes frequently reproduce on biennial or triennial cycles, reflecting the long periods of time required for females to replenish energy reserves after parturition to fuel subsequent reproduction (Brown, 1991;Bonnet et al, 2002;Pleguezuelos et al, 2007).…”

“…Isolated highland populations occur in the Central Plateau and Volcanic Belt, between 218N and 268N, at elevations between 2,230 m and 2,700 m asl, in the states of Michoacá n, Aguascalientes, México, and the Distrito Federal (Rossman et al, 1996). Although the latitudinal distribution of T. scaliger is within the limits of the subtropical region, its montane distribution provides an opportunity to study the adaptation of reproductive females to the environmental constraints in such habitats, such as climatic seasonality (e.g., humidity) that strongly influence prey availability (Setser et al, 2010).…”

Sexual differences in head form and diet in a population of Mexican lance-headed rattlesnakes, Crotalus polystictus

“…Snakes used for GM analysis of head morphology were collected during June and July 2006 as part of a long‐term, mark‐recapture study of C. polystictus life history and ecology (Mociño‐Deloya et al ., 2009; Setser et al ., 2010). The field site consisted of a mosaic of pasture, fallow fields, and cropland along the Rio Lerma, State of México, Mexico.…”