Summary: Honda-Sumi (2005)

Cricket songs are species-specific signals important for species recognition, mate choice and male advertisement. Honda-Sumi (2005) compared the calling songs of 3 Japanese crickets to validate the function of acoustic signals (i.e. calling song) as a premating isolation mechanism between sympatric species using playback experiments. Teleogryllus emma is widely distributed and is sympatric with both T. yezoemma (North) and T. taiwanemma (South), while T. yezoemma and T. taiwanemma are allopatric. Hondu-Sumi (2005) compared three temporal parameters, 1 frequency parameter and two structural parameters to test for species divergence in signals and also tested whether female T. taiwanemma distinguish conspecific males. Sympatric species had divergent songs, while allopatric species had similar songs. T. taiwanemma females could discriminate conspecifics (i.e. showed positive phonotaxis). This suggests that, where hybridization is costly, calling song is an important premating isolation barrier in sympatric Teleogryllus species.

Summary: Ahearn et al. 1974

Ahearn et al. (1974) identified two kinds of reproductive isolating mechanisms: 1) premating isolation barriers (in the form of behavioural/ethological isolation); and 2) postmating isolation barriers (male hybrid sterility). They suggest that reproductive isolation arises as a by-product of genetic divergence or is induced by natural selection as a gene exchange barrier. Thus, premating isolation should occur more often between sympatric species. Drosophila heteroneura and D. silvestris are sympatric fly species on the island of Hawaii, while D. planitibia is allopatric on nearby Maui. Ahearn et al. (1974) found pronounced behavioural isolation between the sympatric, but not the allopatric, species. They did note that D. planitibia females do discriminate against D. heteroneura males. Male bybrid sterility is seen in allopatric crosses and is not correlated with behavioural isolation. They suggest that this is expected if premating isolation between closely related species is an ad hoc production of natural selection, while postmating isolation is an incidental result of genetic divergence.

Summary: Olsson et al. (2005)

Animals can learn to associate negative events with environmental stimuli (classical fear conditioning). Race bias and fear condition potentially rely on overlapping neural systems. Therefore, Olsson et al. (2005) aimed to further understanding of basic learning theory and social group interaction by investigating how the mechanisms of fear conditioning apply when humans learn by classical fear conditioning in a sociocultural context. They also assessed whether a bias in fear conditioning extends to social groups defined by race. Prepared fear learning is generally demonstrated as persistence to fear-relevant conditioned stimuli in the learned fear response. They conducted two experiments to test whether fear responses acquired to outgroup and ingroup faces persists during extinction (relative to each other). Their results show that individuals from a racial outgroup are more readily associated with an aversive stimulus. However, Olsson et al. (2005) indicate that this response might be reduced by close, positive interracial contact. They postulate that humans might have evolved a more general preparedness to fear others who are dissimilar to themselves or their social group because such individuals were, historically, more likely to pose a threat.

Summary: Hughes et al. (2010)

It is thought that the human Y chromosome evolved a sex-determining function millions of years ago by gene loss. Given this, theories of decelerating decay predicts that chimpanzee and human male-specific regions on the Y-chromosome (MSY) should not show much divergence. Hughes et al. (2010) accurately and completely sequenced the MSY in the chimpanzee, using large-insert bacterial artificial chromosome clones and iterative mapping and sequencing strategies, in order to compare it to the human MSY. They found differences in sequence structure and gene content, suggesting rapid evolution within the last 6 million years, contrary to the prediction that much divergence should be unlikely. They found that both human and chimp MSY euchromatin is largely comprised of ampliconic and X-degenerate sequence classes but noticed that, while humans have less massive palindromes than chimps, chimps have lost large portions of MSY protein-coding genes and gene families. Hughes et al. (2010) suggest that this divergence in chimp and human MSYs could be driven by four synergistic factors: (1) MSY's role in sperm production; (2) "genetic hitchhiking"; (3) frequent ectopic recombination; and (4) mating behaviour differences. They favour (3): that ectopic recombination between MSY amplicons has sped up MSY structural remodelling in both species. This study is the first to fully compared the Y chromosomes from two closely related species. The importance is two-fold: (1) it provides empirical insight into the evolution of the Y-chromosome; and (2) it provides a test of decelerating decay theories.

Summary: Koboroff et al. (2008)

The two hemispheres of the brain are able to conduct different functions, an ability known as brain lateralization. In birds, brain lateralization has been inferred when a preference to observe a stimulus with one eye ("lateral monocular visual field" is observed. Koboroff et al. (2008) considered that Australian magpies (Gymnorhina tibicen) would show eye preferences when performing anti-predator response. Constant assessment is needed during mobbing behaviour, to make decisions regarding approach, mob or withdraw. They speculated that the left hemisphere would control approach, while the right hemisphere would control withdrawal. However, since mobbing is considered a strong agonistic response, this could be controlled by the right hemisphere (controls intense emotion). Monocular fixations prior to or during performance of mobbing activity in response to perceived predation threat were video recorded. Koboroff et al. (2008) found that, prior to withdrawal, magpies favoured the left eye (85%), while prior to approach, magpies favoured the right eye (72%). Hence, approach in magpies is controlled by the left hemisphere, while withdrawal is favoured by the right hemisphere. They speculate that the left hemisphere is used to process visual inputs prior to approach and the right hemisphere prior to withdrawal. Their results are consistent with hemispheric specialisation in other species, including humans. The relationship between predator-prey interactions and the right hemisphere suggest that the right hemisphere may have, over evolutionary time, organised various anti-predator strategies.

Summary: Sigmund et al. (2010)

Players incur costs when imposing fines on exploiters in 'public goods games'. Even the threat of punishment can increase average pro-social contribution and promote collaborative efforts, yet emergence and stability of costly punishment are problematic. Sigmund et al. (2010) designed a model to compare peer-punishment with pool-punishment, which facilitates the sanctioning of second-order free-riders (those who do not punish exploiters), to determine the most beneficial reward system. The systems are expensive ways to encourage free-riders to cooperate. Spread of second-order free-riders can cause cooperation collapse. Without second-order punishment, the peer-punishment is optimal, but in the presence of second-order punishment, pool-punishers do better. Efficiency is traded for stability. Emergence and stability of costly punishing systems, which regulate common group resources and enforce collaborative efforts, do not require group selection or higher authority prescription. While Sigmund et al. (2010)'s model is minimialistic, it is sound in principle.

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.