Summary: While & Wapstra (2008)

Hatching asynchrony, the time span between hatching of the first and last egg, potentially confers a fitness benefit to offspring and / or parents and decoupling hatching asynchrony hypotheses from those related to onset of parental incubation is important. While & Wapstra (2008) experimentally tested the adaptive nature of hatching asynchrony in a non avian species, Egernia whitii and examined whether there are fitness advantages to offspring in asynchronous birthing. They used arginine vasopressin to manipulate birthing synchrony in female lizards and examined offspring growth and survival. Offspring from asynchronous treatments suffered from higher mortality, but had increased mass at 6 weeks. Offspring from asynchronous clutches also had a higher growth rate. Differences were driven by offspring mass at birth and the development of a greater mass hierarchy in asynchronous litters. It is thought that mortality in asyncrhonous litters was a function of increased aggression between conspecifics, resulting in decreased basking and feeding rates, loss of condition and eventual starvation by one individual. While & Wapstra (2008) found that birthing asynchrony in E. whitii appears removed from the constraints on the production of follicles (asynchronously), ovulation and embryonic development as asynchrony is observed at first at birth. Females of this lizard species exert considerable control over asyncrhonous birthing, suggesting that asynchrony in E. whitii is not simply the result of synchronous developmental constraints. Their results suggest that hatching asynchrony represents a trade-off between the associated costs and benefits.

Summary: Townsend et al. (2010)

Animal vocalisations vary both between individuals and social and behavioural contexts. They also have the potential to differ between groups. Stereotyped group-specific calls, otherwise known as group signatures, may play a role in territory defence or mate choice (called "contact calls"). Meerkats (Suricata suricatta) use close calls to maintain social organisation when foraging, however it is not known whether these call types possess group-specific signatures and whether the information in the calls can be perceived by receivers. Townsend et al. (2010) investigated various questions relating to the close calls produced by meerkats, what the adaptive function of these calls was and whether the information within the calls is perceived by receivers. They found that close calls can be distinguished on the basis of identity and do represent group signatures. However, while the information in these calls codes for group identity, it does not seem to be perceived by receivers, most likely because meerkats use other sensory systems for individual identification of non-group members.

Summary: Albo & Costa (2010)

Nuptial gift giving is rare in spiders, but is known to occur in Paratrechalea ornata (a neotropical spider belong to the family Trechaleidae. Albo & Costa (2010) tested various hypotheses (mating effort, sexual cannibalism and paternal investment) to determine the function of nuptial gift giving. They compared sexual behaviour and reproductive success of pairs in both the presence and absence of a nuptial gift. Historically, it has been suggested the nuptial gifts function as a form of paternal investment. Albo & Costa (2010), however, found that males carrying a prey item had better mating success, longer copulations and longer palpal insertions. Furthermore, longer copulations were associated with earlier eggsac construction and oviposition in females. This suggests that nuptial gift giving represents male mating effort in P. ornata. These gifts could allow males to control duration of copulation, thereby increasing sperm supply and likelihood of paternity.

Summary: Fleming & Luebke (1981)

Nulliparous female rats initially actively avoid pups, whereas parturient females readily respond maternally. Nulliparous females are known to show different behavioural responses to pups, including cannibalism, covering of pups with nesting material and retrieval, although this is rare. More often, nulliparous females seem to treat pups as aversive stimuli. Fleming & Luebke (1981) tested whether nulliparous females are indeed fearful of pups, predicting that these females would show more fear-mediated responses, such as active avoidance, than parturient females. In the first study, they investigated tolerance of nulliparous females and the temporal relationship between pup-avoidance and maternal responding. They found that nulliparous females initially avoided an area with pups, but began responding maternally after 5 days, suggesting that close proximity of pups facilitates maternal responding. In the second study, they investigated that nulliparous females are, in general, more fearful to novel situations than parturient ones. They found that nulliparous females have longer emergence times, spent less time in the open and investigated less, suggesting that they show greater timidity than parturient females. Fleming & Luebke (1981) indicated that reduced emotionality in parturient females could be hormonally mediated. In the third study, they investigated whether this greater timidity was reflected in their social interactions with intruders. They found that nulliparous females were chased more often by intruders. The functional significance of heightened fear and pup avoidance is not clear, however, nulliparous females may respond more cautiously in order to minimize time and investment on young that are not their own.