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.

Summary: Elie et al. (2010)

In birds, vocal duetting is a mutual acoustic joint display, usually made by a mated pair, of temporally coordinated vocalisations (vocal or nonvocal sounds). Elie et al. (2010) investigated whether private vocalisations between pairs of zebra finches (Taeniopygia guttata) could be considered vocal duetting. They recorded meeting sequences (vocal sounds made upon return to the nest) and sentinel sequences (vocal sounds made when one individual was outside the nest) to determine whether these sequences fitted the identified criteria for vocal duetting. They found that meeting sequences were more common when separation period increased, whereas sentinel sequences were more common when separation period decreased. For both sequence types, the number of female and male calls were positively correlated, indicating coordination between mates. Elie et al. (2010) propose that these private calls represent duets. Since partners performed coordinated mutual displays, mutual displays represent vocal duets and may function to mediate pair bond maintenance.

Summary: Clutton-Brock et al. (2006)

For most animals, competition is more intense in the sex that invests less in offspring. However, in some cooperatively breeding species, such as meerkats (Suricata suricatta), females (which normally invest more in care) compete more frequently and intensely. In the case of meerkats, a single dominant female will monopolise reproduction in a group. Clutton-Brock et al. (2006) showed that female meerkats gain greater reproductive benefits from acquiring dominance status and the traits that increase competitive ability also exerted a greater influence on breeding success. Individual differences in breeding success depend on the length of time the individual remains dominant in the group. Clutton-Brock et al. (2006) show that females that reach dominance status have longer breeding tenures and gain greater reproductive benefits than males. They suggest that the greater benefits accrued could explain why females compete so intensely for breeding opportunities. They suggest that the mechanism generating sex differences in reproductive competition in parental investment is not only related to sex differences in parental investment. They also suggest that competition for breeding opportunities influences the evolution of sex differences and how sexual selection operates.

Summary: Smith et al. (2002)

Humans have three types of cone receptor, while birds have four and are sensitive to ultraviolet light (UV). It is thus likely that birds require four primary colours for colour vision and are thus tetrachromatic. Like humans, birds have short, medium and long wavelength sensitive single cones. Birds use UV signals for a number of tasks, such as mate choice and foraging, but few studies have investigated a role for UV in the detection of chromaticity differences. Achromatic mechanisms are involved in the perception of brightness while chromatic mechanisms are responsible for the perception of colour differences. Smith et al. (2002) developed a 'colour blindness' test, which they administered to a passerine, the European starling (Sturnus vulgaris), and a non-passerine, the Japanese quail (Coturnix c. japonica). This was an associative learning technique where the bird had to learn to discriminate between patterns of random intensity with or without UV reflectance. Both species were able to distinguish between orange and red stimuli, and between UV and non-UV stimuli, and were making the discrimination using chromaticity differences, not achromatic cues. This indicates that the output of the UV cone is involved in chromatic colour vision.

Summary: Persaud & Galef (2005)

Generally, females invest more in their offspring than males, therefore they should be more choosy when selecting mates. Furthermore, in species where sexual coercion occurs, females may exert an influence on paternity by selectively voiding or retaining sperm of reproductive partners, which might affect their partner's reproductive success. This is known as postcopulatory or cryptic mate choice. Persaud & Galef (2005) tested whether male Japanese quail (Coturnix japonica) that are preferred by females have higher reproductive success (measured by likelihood of egg fertilization) than males that are not preferred by females. They also tested whether a male's reproductive success could be increased if a female observed him courting and mating with another female. They found that males that are preferred by females have a greater likelihood of fertilizing her eggs and that a female's preference could be enhanced by her observations of male mating behaviour. In addition, choosing a male that had courted and mated previously increased his likelihood of successfully fertilizing another female's eggs. Furthermore, females can identify males that are more likely to inseminate them and can exert a degree of control over which male will fertilize her eggs, thereby influencing both paternity and a male's reproductive success. The results suggest that female Japanese quail can exercise postcopulatory mate choice and that female preference can directly or indirectly affect a male's fertilization success.

Summary: Viellette & Reebs (2010)

Syrian hamsters (Misocricetus auratus) are used extensitvely in biomedical and behavioural research, but many aspects of hamster welfare remain open to study. Replacing soiled bedding is standard animal husbandry practice, but the how often this should be done is still questionable, as cage cleaning can induce stress. Veillette & Reebs (2010) tested whether Syrian hamsters prefer new bedding in contrast to soiled, lived-in bedding for nesting and they also assessed the relative value of shelters. They used 15 male and 15 female animals, none of which have previous experience with shelters. Most male and female hamsters favoured the old cage over the new, regardless of the presence of a shelter, and the majority of male hamsters (and some females) never nested in the new cage. Their results suggest that nesting hamsters show low motivation for a cage with new bedding and they value shelters. Veillette & Reebs (2010) indicate that the standard husbandry practice of weekly cleaning may only be justified on the basis of sanitary and health considerations.

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.

Summary: Rivera-Gutierrez et al. (2010)

Birdsong, a multifaceted signal consisting of many traits (each under sexual selection pressure), plays an important role in both female mate choice and male-male competition. 3 hypotheses have been proposed to explain the expression of these traits: 1) one trait signals one aspect of male quality, therefore many traits represent a multidimensional message (multiple-messages hypothesis); 2) each trait signals only partial information, therefore many traits signal redundant information (redundant-signal hypothesis); 3) traits do not provide reliable information about male quality but are retained because they are not costly to produce (unreliable-information hypothesis). Rivera-Gutierrez et al. (2010) investigated whether the various components of song of 58 great tits (Parus major) was expressed differently in relation to 3 indicators of male quality (age, condition survival). They found support for all 3 hypotheses, concluding that great tit song is a multidimensional signal conveying multiple, redundant and unreliable information about male quality.

Summary: Sobel et. al (2001)

Parkinson's disease is a disorder characterised by a progressive loss of neuronal structure or function. It has a primary influence on motor control, although Parkinson's disease may also affect both cognitive and sensory processing. Patients with Parkinson's disease have recognised olfactory impairments, however, Sobel et al. (2001) suggest that this is partly a sniffing impairment. Whereas olfaction integrates both sensory and motor information, sniffing is primarily a physical or motor action. Sobel et al. (2001) tested 40 people (20 with Parkinson's and 20 age-matched healthy controls) in four olfactory tests and found that people with Parkinson's disease at lower sniff airflow rate and volume, thus were impaired at sniffing. This suggests that sniffing is a vital component of human olfaction and is thus an important component of the olfactory impairment seen in Parkinson's disease patients.

Summary: Thünken et al. 2010

Offspring survival and future reproduction can be enhanced through the provision of parental care, which also serves to increase the inclusive fitness of the parents. Parental investment theory predicts that parents should alter the level of care they provide to young based on the quality of the brood (i.e. the reproductive value) and should trade-off current investment with future care if this is likely to enhance their own lifetime reproductive success. Thünken et al. (2010) investigated this theory in the cichlid fish Pelvicachromis taeniatus, a species characterised by intense biparental brood care. They manipulated offspring quality by altering food availability (not for adults) and compared the response of parents to offspring over a period of 4 weeks. Although females generally showed higher levels of care than males, overall parental care decreased with time as offspring matured and became less vulnerable to predation. Interestingly, parents of low-quality broods (smaller average body size) showed a greater reduction in care than parents of high-quality broods, providing support for parental investment theory. Furthermore, females raising high-quality broods were more aggressive to their mating partners than females raising low-quality broods. By adjusting care relative to brood quality, parents can conserve energy for subsequent reproductive events.

Summary: Ramm & Stockley (2009)

Sperm competition theory predicts that males will respond to an increased risk of sperm competition from rivals by increasing sperm allocation and predicts that the increase in allocation will be lower when rivals are related. Furthermore, scent-based cues could provide information on the presence and identity of conspecifics and could serve as a basis for adjusting sperm allocation. Ramm & Stockley (2009) investigated whether male house mice (Mus musculus domesticus) adjust sperm allocation in response to odour-based cues of rival males present in the environment and whether they vary sperm allocation decisions according to the relatedness of rival males. In contrast to the predictions made by sperm competition theory, Ramm & Stockley (2009) found no evidence that male house mice adjust the number of sperm allocated to an ejaculate in response to odour-based cues of immediate sperm competition risk, even though male mice were sensitive to the odour cues from rival males. They suggest that the response to cues of sperm competition risk may display considerable interspecific variability.