Summary: Butlin (1995)

The reinforcement hypothesis suggests that natural selection favours an increase in assortative mating (and thus progress towards speciation, if two divergent populations produce low fitness hybrids in the zone of contact. Butlin (1995) briefly reviews a model proposed by Liou & Price (1994) and an empirical study by Noor (1994). Liou & Price's (1994) study considered secondary contact in sympatry of two divergent stickleback populations, with three possible model outcomes (extinction of one population, permanent mixing of the gene pools or reinforcement and speciation). The model suggested  that reinforcement is likely because the diluting effects of gene flow are absent. Butlin (1995) notes, however, that Liou and Price (1995) did not distinguish between the conditions of zero hybrid fitness and reinforcement and argues that the most questionable aspect of this model is the genetic basis of selection against hybrids. Noor's (1994) study addresses the situation where there is a very low level of gene exchange between two species of Drosophila, finding that hybrid males were sterile but hybrid females were fertile. Noor (1994) found evidence for reinforcement, however, Butlin (1995) notes that, while the result is exciting because of testability, the observation is no stronger evidence for reinforcement than other examples. He does agree that this approach could provide more discriminating predictions, but a larger number of localities has to be examined. Finally, Butlin (1995) indicates that reinforcement is potentially important evolutionary process and suggests that further work will identify it's actual importance.

Summary: Kalueff & Tuohimaa (2005)

Grooming is an innate behaviour represented across most animal species. It is a rich source of behavioural and biological information and forms an important part of the rodent behavioural repertoire. Mice show strain differences in their behavioural phenotypes, particularly in grooming behaviour. Various stressors and genetic manipulations alter mouse grooming. Kalueff & Tuohimaa (2005) defined behavioural differences and organisation in spontaneous grooming activity (novelty-induced) between three strains (129S1, NMRI, BALB/c) of laboratory mice. All three strains showed contrasting grooming phenotypes. 129S1 showed lower grooming activity and impaired microstructure, accompanied by lower vertical exploration. BALB/c and NMRI mice showed higher vertical activity and unimpaired grooming microstructure, and BALB/c mice showed higher grooming levels. Kalueff & Tuohimaa's (2005) study suggests that contrasting grooming phenotypes may not be due to strain differences in their sensory abilities, general activity levels, brain anatomy or aggressiveness, but rather reflects a complex interplay between anxiety, motor and displacement activity in these strains. They suggest that an in-depth ethological analysis of mouse grooming may be a useful tool in neurobehavioural research and could contribute to our understanding of behavioural disorders in humans.

Summary: Dingemanse et al. (2007)

Animal populations show individual differences in suites of correlated behaviours ("temperament", "animal personality") across different contexts ("behavioural syndromes"). Population variation in behavioural syndrome may exist for two reasons: 1) natural selection favours covariance in a trait and syndromes will evolve in response ("adaptive hypothesis"); and 2) stochastic processes (e.g. mutation, drift, founder effects, gene flow) maintain variation. Dingemanse et al. (2007) examined the adaptive hypothesis using a comparative approach. They measured 5 different behaviours (categories: aggression, general activity, exploration-avoidance-novel foods, novel or altered environments) across 12 different populations (6 predator-sympatric, 6 predator-naive) of three-spined stickleback (Gasterosteus aculeatus) and assessed whether the differences in behaviour varied consistently depending on the environment. Their results confirm the prediction of the adaptive hypothesis. They found that behavioural syndromes are not always the same in different types of population, implying that population variation in behavioural syndromes is not a result of stochastic evolutionary processes. They suggest that, in sticklebacks, behavioural syndromes are correlated with the presence of predators. Dingemanse et al. (2007) suggest that behavioural syndromes are not fixed according to physiological or genetic constraints and arise from adaptive evolution, where a behaviour is favoured because it is the most optimal trait in that environment.

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.