Summary: Merkle & Wehner (2009)

Foraging desert ants, Cataglyphis fortis, do not rely on chemical cues when searching for their nest, but rather navigate using path integration. In this process, all directions steered and covered for all movements are summed, providing ants with a home vector that leads them back to the nest on a straight path. Ants also use landmark information to adjust their movements as the path integrator is prone to error. Ants engage in systematic search behaviour if they do not encounter the nest entrance at the position suggested by the path integrator. Merkle & Wehner (2009) investigated whether additional cues influence the systematic search patterns of desert ants or whether this is exclusively determined by distance travelled. They captured ants at different points during inbound journeys or when about to enter the nest. Ants were then transferred to an unfamiliar test area and their paths recorded. Merkle & Wehner (2009) found that searches were influenced by distance covered, as well as other factors, but certainty of nest location increased with closeness to the nest. Most inbound ants, regardless of distance, continued the remaining part of their runs and then commenced their nest search, whereas those captured at the nest entrance started searching for the nest immediately. They suggest that the ants' systematic search behaviour does not depend only on the length of the foraging trip, but is more flexible than previously thought.

Summary: Bonato et al. (2009)

Female birds invest more in reproduction than males, due to egg production. Therefore, females should change their investment in any one breeding attempt in relation to the probability of it succeeding. Females of many species favour mating with males that show elaborate ornamentation, possibly because ornamentation is an indicator of male quality. Thus, females should invest more in more ornamented males. Egg size is a good indicator of maternal investment and chicks hatched from larger eggs growth faster and have a higher chance of survival. Bonato et al. (2009) investigated the relationship between male colouration (measured using UV-visible range spectrophotometry) and egg mass in male ostriches (Struthio camelus). They assessed paternity of eggs using microsatellite markers. Female ostriches discriminate between males on the basis of ornamentation and some features of male colouration (neck colour, white and black body feathers and brightness of black feathers) are good predictors of egg mass. Bonato et al. (2009) suggest that these visual cues influence female perception of male quality and females adjust their level of maternal investment as a result. Their study has important implications for the ostrich farming industry, where hatching success is notoriously low.

Summary: Adams & Rohlf (2000)

Ecological character displacement describes the differences in morphology that occur between sympatric species due to interspecific competition, which allows them to coexist. In this study, Adams & Rohlf (2000) describe ecological character displacement between 2 terrestrial salamander species, Plethodon cinereus and P. hoffmani from two geographic transects in the USA. They quantified morphology of individuals from both allopatric and sympatric populations using linear measurements and landmark-based geometric morphometric methods. They also quantified food resource use by assaying stomach contents. Adams and Rohlf (2000) found morphological differences between sympatric, but not allopatric, populations in terms of prey consumption and segregation of prey according to size, although the resource bases for each population were similar. The reduction in prey consumption implied competition for food resources. The major anatomical difference was in relation to the functional and biomechanical properties of jaw closure. P. hoffmani has a faster, but weaker, jaw in contrast to P. cinereus, which has a slower but more powerful jaw. Adams & Rohlf's (2000) findings provide evidence that character displacement could the causal mechanism driving morphological differences between sympatric populations and provides an example of how anatomical differences can be identified among populations using geometric morphometrics.

Summary: Makowska et al. (2009)

Laboratory mice are the most commonly used species in biomedical research and are most commonly euthensased with carbon dioxide, which they may find aversive, as has been shown in rats. In many countries, Animal care policies generally require death to be painless and there should be minimal fear and anxiety. Makowska et al. (2009) assessed male CD-1 mouse aversion to CO2 usuing approach-avoidance testing in response to CO2 and 4 alternatives (argon, CO, halothane and isoflurane). Mouse motivation to avoid gas exposure was measured against motiavtion to assess a highly palatable sweet food reward. During preliminary testing, they recorded time to recumbency and concentration of gas at recumbency. Mice were trained to enter the test chamber through provision of a piece of sweetened shredded coconut as a reward presented in response to gentle tapping of the cage. When exposed to CO2, argon and CO, mice always left the test cage before losing consciousness, showing that mice forego access to a preferred food reward in the presence of the gas. In most cases, when exposed to halothane and isoflurane, mice also left the test cage before losing consciousness, however motivation to avoid isoflurance appeared weaker. Makowska et al. (2009) suggest that dyspnea is the cause of the aversion to CO2. Furthermore, they suggest that all substances tested were aversive to mice, therefore the test for a non-aversive agent should continue. They also suggest that, as isoflurane appears to be the least aversive, it should be used (at least in the interim) as the preferred alternative to CO2 or other gases.

Summary: Wiltgen et al. 2010

The hippocampus is important for the temporary formation and retrieval of episodic and contextual memories. Damage to this area produces amnesia for new memories. Wiltgen et al. (2010) examined the relationship between memory quality and hippocampus dependency, hypothesizing that memory quality may be critical for determining whether the hippocampus is essential for memory retrieval. Using immediate early gene expression (as measured by RT-PCR), they monitored hippocampal activity in mice during memory retrieval and found that detailed memories require the hippocampus, whereas memories that lose precision do not. The dorsal hippocampus is preferentially activated by retrieval of detailed contextual fear memories and is necessary for the retrieval of detailed memories using a context-generalization procedure. Wiltgen et al. (2010) suggest that detailed contextual memories require the hippocampus, providing a new framework for understanding memory consolidation. Their data help to establish the precise role of the hippocampus in memory retrieval.

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.