Description
Maternal attendance of newborn snakes is ubiquitous among temperate pitviper species, yet few studies have focused on any aspect of this behavior. In general, female pitvipers remain at the birth site with their young until neonates complete their first shed cycle ('ecdysis'), after which the mother and neonates disperse. The goals of this research were to determine if fitness benefits are conveyed to neonates during the maternal attendance period and to examine the hormonal mechanisms mediating attendance behavior. Pregnant female cottonmouths (Agkistrodon piscivorus) were collected from the wild and used in captive behavioral studies. All studies involved comparisons among two treatment groups: (1) 'Maternal Attendance' (MA) - females were allowed a normal maternal attendance period, where neonates were left with the mother until they completed ecdysis, after which they were removed, and (2) 'Separated' (SE) - females had their neonates removed shortly after birth. Chapter 1 focused on the effect of maternal attendance on kin discrimination. The relatedness between individuals can have strong effects on behavioral interactions, as engaging in mutually beneficial behaviors with kin can increase inclusive fitness. Parental care has been shown to be particularly important for kin discrimination in birds and mammals, but similar studies have not been conducted on species exhibiting more rudimentary forms of parental care. We measured the affiliative behavior of related and unrelated juvenile-juvenile and mother-juvenile pairs that had been allowed a maternal attendance period (MA) or had been separated at birth (SE). We found that maternal attendance was not required for sibling or mother-offspring recognition, per se, but did enhance female affiliative behavior overall, and particularly that of sisters. In contrast, post-birth separation had only a modest effect on mother-juvenile affiliative behavior, and no effect on the strong affiliation between mothers and daughters. The patterns of affiliative behavior observed in maternally-attended snakes corresponded to results of previous studies on pitvipers; however, the behavior of juveniles separated at birth did not. Thus, it is possible that maternal attendance plays some role in the development of adaptive affiliative behavior in pitvipers. Chapter 2 focused on the effect of neonate presence on maternal antipredator behavior. One of the primary functions of parental care is the protection of offspring from predators, and parents of diverse taxa are able to carefully modulate their antipredator behavior when offspring are present. We simulated predator encounters and recorded the antipredator behavior of females in three treatment groups (MA, SE, and non-reproductive (NR) females). The first trial occurred while MA females were attending neonates and the second trial after neonates had been removed; SE and NR females were also tried twice. When mothers were attending offspring, they were more hesitant to engage the predator and were less aggressive once they did, relative to SE and NR females. When these same mothers were no longer attending offspring, they significantly increased their antipredator behavior by engaging the predator quickly and displaying more aggressive behaviors. This behavioral change was not observed in SE or NR females, indicating that mothers were modulating their antipredator behavior in the presence of neonates. Chapter 3 focused on the hormonal mechanisms mediating attendance behavior. Steroid hormones have been well-documented to regulate many aspects of reproductive physiology and behavior, including parental care, but no studies have determined if maternal attendance behavior in pitvipers is similarly regulated. Serial blood samples were collected from MA females at five time points during and after maternal attendance; SE females had samples collected on a similar temporal schedule. Plasma levels of progesterone (P), estradiol (E), testosterone (T), and corticosterone (CORT) were measured. The overall pattern of P, E, or T did not significantly differ between MA and SE females. MA females exhibited a significant peak in CORT on the day that neonates shed, but this peak was not observed in SE females. It is possible that the elevated CORT observed in MA females was stimulated by the increased activity and/or changing chemical cues of shedding neonates. Because free-ranging pitvipers cease attending neonates at the completion of the post-natal shed cycle, we hypothesize that CORT might play an integral role in signaling females to terminate attendance behavior. Overall, our results provide limited evidence that maternal attendance might function to enhance adaptive kin discrimination and protect neonates from predation, and that certain aspects of attendance behavior are hormonally mediated.
