Amando Bautista

Development of behavior in the litter huddle in rat pups: Within- and between-litter differences

Early postnatal growth in mammals can be considerably influenced by litter size and often differs among littermates in relation to birth mass. In a study of Long Evans laboratory rats we asked whether within- and between-litter differences in body mass and growth are related to behavioral development during early postnatal life. For this, we analyzed the amount of general motor activity and the display of directed, seemingly goal-oriented interactions within the litter huddle in previsual pups. During the study period from postnatal days 2 to 11, we found significant changes in pup behavior, showing a nonlinear, quadratic shape. General motor activity and, more specifically, the display of behaviors apparently directed to reaching central positions in the litter huddle increased during the first postnatal days and then decreased again. However, pups from small litters that grow more rapidly than pups from large litters, showed a faster increase in both behaviors, whereas the young from large litters reached a higher maximum. We also found striking within-litter differences in the amount of directed behavior performed by light and heavy pups, with higher levels in the former group, most probably because light pups that have a less favorable body mass-to-volume ratio and more often occupy peripheral positions in the litter huddle, make a greater effort to reach thermally favorable central positions. In conclusion, our study shows there to be consistent between-litter as well as within-litter differences in behavioral patterns during early life. These differences might have important implications for an individuals long-term behavioral and physiological performance.

Littermate presence enhances motor development, weight gain and competitive ability in newborn and juvenile domestic rabbits

Interest has been growing in the influence siblings may have on individual development. While mammalian research has tended to emphasize competition among siblings for essential but often limited resources such as the mothers milk, there is also evidence of mutual benefits to be had from sibling presence, most notably for altricial young in enhanced thermoregulatory efficiency. In the present study we asked whether littermates of an altricial mammal, the domestic rabbit, might gain other developmental benefits from sibling presence. From postnatal days 1 to 25 we raised rabbit pups either together with their littermates or alone except for the brief, once daily nursing characteristic of this species, while controlling for litter size and ambient nest box temperature. At weaning on Day 25 the young were then transferred to individual cages. Before weaning, we found that pups raised separately from their littermates obtained less milk, and showed lower weight gain and slower development of the ability to maintain body equilibrium than their litter-raised sibs. This was the case even though the two groups did not differ in birth weight or in the ratio of converting milk into body mass in their temperature-controlled nest boxes. Postweaning, the isolation-raised animals were also less successful in competing for food and water when tested after deprivation than their litter-raised sibs. The present study adds to the growing evidence of the influence, in this case positive, that sibs (or half sibs) may have in shaping one anothers development.

Mother-Young and Within-Litter Relations in the European Rabbit Oryctolagus cuniculus

The European rabbit, Oryctolagus cuniculus, in its domesticated form, is an important animal in biomedical research and in a number of countries is of economic significance for the production of meat and fur. In the wild, it is an appreciated game species, and in several countries it is also a major agricultural pest. The rabbit’s long association with humans has resulted in a large body of information on its general biology and it is now one of the most studied mammals in the wild. In whatever context, however, the rabbit is best known for its remarkable reproductive capacity. This is due in large part to the reproductive efficiency of the female (Fig. 1), a notable feature of which is the brief time mothers spend each day even with their newborn young (reviewed in Hudson and Distel 1982; 1989). After giving birth to the altricial young in a separate nursery burrow or in a chamber in the colony warren, the doe leaves, closes the entrance, and only returns to nurse for a few minutes once approximately every 24 h. As for several other lagomorphs (see below), such limited contact between mother and young is thought to have evolved to reduce the possibility of predators locating the nest from the attendance of the more conspicuous mother (Zarrow et al. 1965). Rabbits have a postpartum oestrus and usually mate again soon after giving birth. If this results in a further pregnancy, the doe abruptly weans the young she is currently nursing on about postnatal day 26 in preparation for the birth of the next litter (reviewed in Hudson et al. 1995a; 1996; Martinez-Gomez et al. 2004). This, for a mammal, unusually limited maternal care is made possible by a number of behavioural and physiological specialisations of mothers and young. It also makes it possible to study interactions among littermates and to explore the consequences of these for development, survival, and later reproductive success, without the complicating factor of the mother’s presence. In this chapter we review current knowledge of the mother–young relationship,

Competition in newborn rabbits for thermally advantageous positions in the litter huddle is associated with individual differences in brown fat metabolism

The altricial young of the European rabbit (Oryctolagus cuniculus) are not brooded by the mother, and although they are born into an underground nest, depend importantly on the warmth and insulation provided by littermates for their early growth and survival. Consistent with previous studies, heavier pups occupied more central, thermally advantageous positions in the litter huddle, maintained higher body temperatures, obtained more milk, were more efficient at converting it to body mass, and consequently grew faster than their lighter sibs occupying the periphery of the huddle. In the present study we measured the expression of uncoupling protein 1 (UCP-1), which is essential for the metabolism of brown adipose tissue to generate body heat in response to cold. In nine litters of domestic rabbits maintained for the first four postnatal days at temperatures below their critical thermoneutral temperature, peripheral pups showed greater expression of UCP-1 than intermediate pups, and these greater expression than central pups. This suggests that during early development littermates of the rabbit experience differing degrees of activation of the sympathetic nervous system as a consequence of exposure to different thermal environments associated with different positions in the litter huddle. Whether this is associated with long term differences in the physiological response to cold and perhaps in the manner of responding to other environmental challenges is currently under investigation.

Smell, Suck, Survive: Chemical Signals and Suckling in the Rabbit, Cat, and Dog

All mammalian young depend for their survival for at least some period on the mother’s milk. Locating the mammary region, attaching to a nipple or teat, and being motivated to suck until milk flows is one of the first and most vital challenges they face. For altricial species such as the European rabbit (Oryctolagus cuniculus), the cat (Felis silvestris catus) and the dog (Canis lupus familiaris) born without vision, not directly aided by the mother, and having to compete with littermates, the challenge is particularly great. All three species use chemical cues apparently emitted under hormonal control by lactating females to achieve this. From birth they quickly orient to the mother’s ventrum, rapidly locate nipples, and respond with nipple-search behavior and nipple attachment to other lactating females but not to non-lactating females. Kittens, but not rabbits or puppies, also quickly establish a nipple order in which each kitten uses primarily one or sometimes two particular nipples. Recognition of own nipples appears to depend on learned olfactory cues, possibly contained in each kitten’s own saliva. These three species illustrate similarities and differences in the use of chemical cues by mammalian young in the suckling context and raise questions warranting further investigation: are there commonalities in the origin and chemical composition of the suckling signals emitted by the mothers of such taxonomically different species? Are there commonalities in the neural processing of such signals, for example, in the participation of the main and accessory olfactory systems? To what extent are inborn responses augmented or even replaced by learned chemical cues? And does the early experience of such cues affect the response to chemical signals in later life?

No reliable evidence for immediate noise-induced song flexibility in a suboscine

Vermilion flycatchers, a suboscine, sing songs with more elements in territories with higher urban noise levels. We tested the hypothesis that this pattern is achieved through vocal flexibility, by which individuals add elements to their songs when noise increases; we also tested whether males modulate other song attributes and song output with noise. To this end, we did a playback experiment with free-living males where we recorded their songs during three noise treatments: first ambient noise (FAN), high urban noise (HUN), and second ambient noise (SAN) treatments. We counted the number of song elements and measured acoustic attributes both in the whole song and in the song terminal element (T). Males did not modify the number of song elements, nor song minimum frequency, with noise. The T minimum frequency slightly increased during SAN when compared to the FAN and HUN treatments, but it did not differ between the HUN and FAN treatments. Thus, we interpret these results as a lack of reliable evidence of immediate noise-induced song flexibility in frequency parameters. Song entropy decayed during the trials, but this seemed to be an effect of time and not a noise-induced change. Vermilion flycatchers appear to be less capable of modulating spectral song attributes to cope with noise than many oscines. We discuss other potential strategies that this species may use to deal with noise and a possible mechanism by which males end up singing longer songs in noisier territories (natural selection).

Response of two sympatric carnivores to human disturbances of their habitat: the bobcat and coyote

Information about human land uses, producing the least impact on wildlife and their habitats, is crucial to develop management strategies allowing coexistence between human beings and wildlife. We investigated the responses of the bobcat (Lynx rufus) and the coyote (Canis latrans) to different types of human activity by assessing the abundance, habitat use, and activity patterns of these species in response to extraction of firewood, grazing, and crop farming within their habitat. Photographic records of both carnivores were obtained from 18 camera-trap stations, distributed evenly within these three types of habitat disturbances. The highest relative abundance index for both carnivores was obtained at firewood extraction sites, followed by grazing sites, and croplands. The probability of carnivore sightings varied between species by type of disturbance and by season. The probability of bobcat sightings was highest within firewood extraction sites, with no effect of season, whereas that of the coyote was highest during winter, with no effect of type of human disturbance. An analysis of habitat use revealed that both carnivores avoided cropland sites. Activity patterns were similar, which suggests an absence of temporal segregation between these species; moreover, the activity patterns of both carnivores seems to be affected by intensity of human activities. Preference for woodland habitats by both carnivores denotes that firewood extraction is the disturbance that least affects bobcat and coyote populations; therefore, this kind of human activity could be the least impacting type of disturbance for the coexistence between humans and these carnivore species.