Summary: Tsai et al. (2009)

Dopaminergic (DA) neurons are intrinsically involved in motivated behaviours and dopamine signalling can be altered by natural rewards and drugs of abuse. Changes in the firing patterns of these neurons could elicit reward-related behaviours, however, it in unclear whether this alone is sufficient to induce a response. Tsai et al. (2009) used a Cre-inducible adeno-associated virus vector carrying a gene encoding the light-activated cation channel, channelrhodopsin-2 (ChR2) to selectively control DA neurons in freely behaving mammals. They found that ChR2-EYFP co-localises with endogenous TH in coronal VTA sections. They also used whole-cell patch clamps to assess the potential for optogenetic control of transduced cells. ChR2-EYFP-expressing cells showed electrophysiological properties typical of DA neurons, indicating that ChR2 expression alone can not alter basic physiology. They also tested for behavioural conditioning effects of phasic DA neuron activity in mice and found that mice developed a clear place preference associated with phasic optical stimulation. These results show that DA neuron activity can be selectively regulated and demonstrate that phasic dopaminergic activity can mediate behavioural conditioning in mammals.

Summary: Widemo & Sæther (1999)

Individuals differ in (most often) predictable ways. However, many studies investigating mate choice and mating preferences have often ignored individual variation in mating preferences, blaming this variation on errors in mate assessment, limited availability of mates or even poor observational or experimental methods. Widemo & Sæther (1999) suggest that an understanding of individual variation in mating preferences is necessary to make predictions about evolutionary change and is crucial for advancing understanding of the processes of mate choice and sexual selection. They suggest that mate choice behaviour will evolve when access to mates, or the resources they provide, are limited by the reproductive success (females) or the number of available mates (males). Furthermore, the outcomes of mate choice depend on individual mating preferences and the extent of their expression and these preferences are determined by preference functions and the degree of choosiness of individuals. Widemo & Saether (1999) regarded preference functions as being determined by ‘innate predispositions’ or flexible reference templates, or a combination of both, and suggest that individual differences in preference functions could result from phenotypic differences in sensory apparatus. Preference functions can indicate the potential for selection on a preferred trait. Choosiness is a trait that is dependent on the physiological condition of the individual and environmental and social factors. These constraints can affect the expression of preference functions. The shape of the preference function and the mate sampling tactic of an individual interact because mate-sampling tactics rely on threshold criteria for acceptance or rejection of mates. Widemo & Sæther (1999) note that to understand variation in mating preferences, there needs to be an awareness of the cues used and their relative importance.

Summary: White et al. (2010)

Morphological and behavioural traits can be influenced by the social environment and, if selected for, these traits may confer specific reproductive advantages to individuals. White et al. (2010) examined whether exposure to more complex social environments improves competitive skills, that could lead to increased reproductive success in adult brown-headed cowbirds (Molothrus ater). They housed some birds in flocks where group members regularly changed (dynamic flocks) and housed other birds in flocks where group members remained constant (stable flocks). They then measured singing and courtship behaviours for all males within these groups. White et al. (2010) found that males housed in dynamic flocks had larger and more variable singing networks and also showed a higher mating success than males housed in stable flocks. Their results suggest that social skills are extremely flexible and indicate a link between reproductive success and social behaviour and competency.

Summary: McCarty & Southwick (1977)

The physical and behavioural development of young mammals can be influenced by characteristics of the preweaning environment, particularly interactions with parents. Cross-fostering young (shortly after birth) between strains or species allows these parental influences to be assessed. If the behaviour of an offspring is similar to that of its foster parents, and is different to that of other individuals raised by their natural parents, it is suggested that parental interactions influence that behaviour. McCarty & Southwick (1977) examined the influence of cross-fostering on olfactory preferences in two species of mouse, the southern grasshopper mouse (Onychomys torridus) and the white-footed mouse (Peromyscus leucopus). Young were either cross-fostered or raised by their natural parents. 1 male and 1 female from each litter were then assessed in an olfactory preference task, where they were exposed to the odour of an opposite sex adult from each species. They found that both southern grasshopper mice and white-footed mice raised by their natural parents showed a preference for the odour of conspecific adults, whereas mice raised by foster white-footed mouse parents showed a preference for the odour of the heterospecific adults. They suggest that there is an interaction between the underlying genotype and preweaning parental interaction that influences the development of species-characteristic odour preferences.