A comparison of bats and rodents as reservoirs of zoonotic viruses: are bats special?

Bats are the natural reservoirs of a number of high-impact viral zoonoses. We present a quantitative analysis to address the hypothesis that bats are unique in their propensity to host zoonotic viruses based on a comparison with rodents, another important host order. We found that bats indeed host more zoonotic viruses per species than rodents, and we identified life-history and ecological factors that promote zoonotic viral richness. More zoonotic viruses are hosted by species whose distributions overlap with a greater number of other species in the same taxonomic order (sympatry). Specifically in bats, there was evidence for increased zoonotic viral richness in species with smaller litters (one young), greater longevity and more litters per year. Furthermore, our results point to a new hypothesis to explain in part why bats host more zoonotic viruses per species: the stronger effect of sympatry in bats and more viruses shared between bat species suggests that interspecific transmission is more prevalent among bats than among rodents. Although bats host more zoonotic viruses per species, the total number of zoonotic viruses identified in bats (61) was lower than in rodents (68), a result of there being approximately twice the number of rodent species as bat species. Therefore, rodents should still be a serious concern as reservoirs of emerging viruses. These findings shed light on disease emergence and perpetuation mechanisms and may help lead to a predictive framework for identifying future emerging infectious virus reservoirs.

Aromatase inhibition during adolescence reduces adult sexual and paternal behavior in the biparental dwarf hamster Phodopus campbelli.

Previous studies have failed to identify an activational role for estradiol in the paternal behavior of Phodopus campbelli fathers. However, none of these studies addressed a developmental role that estradiol might play in establishing paternal behavior in this species. Males were orally administered the aromatase inhibitor letrozole (1 mg/kg/day) for three days at 18, 34, or 90 days of age. As adults, males were tested for paternal and sexual behavior. Letrozole treatment at 18 days resulted in males that spent less time huddling over pups during the birth, and had higher pup losses and male-biased pup survival for the first litter. Letrozole treatment at 34 days resulted in males that had altered sexual behavior; males had a longer interval between mounts and between intromissions, and took longer to achieve ejaculations over the first three ejaculatory series. Furthermore, these males sired smaller first litters and produced second litters with a male-biased sex ratio. Males treated with letrozole as adults showed a modest increase in paternal care during the birth, but pup development and survival were not altered. There was no effect of treatment on attack or retrieval behavior either as sexually naive adults or as new fathers. Thus, the results of the present study suggest that estradiol acts during adolescence to establish the normal expression of midwifery behavior and sexual behavior during adulthood.

Neither reduced photoperiod, nor female-related social cues, nor increased maternal thermal stress result in a paternally responsive Phodopus sungorus male.

Neither reduced photoperiod, nor female-related social cues, nor increased maternal thermal stress result in a paternally responsive Phodopus sungorus male. Physiol Behav [Volume # (Issue #)] 000-000, 2006. -Under laboratory conditions, P. sungorus males are not needed for pup survival and growth and are unresponsive to an experimentally displaced pup. However, males have been found with young pups late in the breeding season, and other laboratories have found evidence for biparental care. Thus, paternal behavior might be expressed in response to relevant social and environmental cues. Reduced photoperiod (from 14L:10D to 12L:12D), increased ambient temperature (from 18 to 23 degrees C) and pairing with an obligate biparental heterospecific female (to remove behavioral barriers to pup contact) were tested. Although within-animal responsiveness during a standardized pup displacement increased under reduced photoperiod, and pup retrieval occurred more often in the heterospecific pairing, paternal responsiveness scores remained negative, and typical of the species, rather than positive, and indicative of paternal responsiveness. Thus, P. sungorus males did not meet criteria for paternal responsiveness in terms of nest attendance, retrieval rates, or positive paternal responsiveness scores. Pup survival and development were not affected. In spite of their seasonal proximity to pups, there is no evidence that these environmental cues and manipulations are sufficient to result in biparental care.

Personality variation in little brown bats.

Animal personality or temperament refers to individual differences in behaviour that are repeatable over time and across contexts. Personality has been linked to life-history traits, energetic traits and fitness, with implications for the evolution of behaviour. Personality has been quantified for a range of taxa (e.g., fish, songbirds, small mammals) but, so far, there has been little work on personality in bats, despite their diversity and potential as a model taxon for comparative studies. We used a novel environment test to quantify personality in little brown bats (Myotis lucifugus) and assess the short-term repeatability of a range of behaviours. We tested the hypothesis that development influences values of personality traits and predicted that trait values associated with activity would increase between newly volant, pre-weaning young-of-the-year (YOY) and more mature, self-sufficient YOY. We identified personality dimensions that were consistent with past studies of other taxa and found that these traits were repeatable over a 24-hour period. Consistent with our prediction, older YOY captured at a fall swarming site prior to hibernation had higher activity scores than younger YOY bats captured at a maternity colony, suggesting that personality traits vary as development progresses in YOY bats. Thus, we found evidence of short-term consistency of personality within individuals but with the potential for temporal flexibility of traits, depending on age.

Paternal care in rodents: weakening support for hormonal regulation of the transition to behavioral fatherhood in rodent animal models of biparental care.

Male rodents that are naturally paternal, like all females, must inhibit infanticide and activate direct parental behavior as they become parents. Males, however, alter their behavior in the absence of parturition, postpartum ovulation and lactation, and therefore do not experience the hormone dynamics associated with such conditions. Paternal males might nevertheless use the same hormones to activate pre-existing maternal behavior pathways in the brain. Positive and inverse associations between prolactin, sex steroids (estradiol, testosterone, progesterone), glucocorticoids, oxytocin and vasopressin and paternal behavior are reviewed. Across biparental rodents (Phodopus campbelli, Peromyscus californicus, Microtus ochrogaster, and Meriones unguiculatus), as well as non-human primates and men, hormone-behavior associations are broadly supported. However, experimental manipulations (largely restricted to P. campbelli) suggest that the co-variation of hormones and paternal behavior is not causal in paternal behavior. Perhaps the hormone-behavior associations shared by P. campbelli and other paternal males are important for other challenges at the same time as fatherhood (e.g., mating during the postpartum estrus). On the other hand, each paternal species might, instead, have unique neuroendocrine pathways to parental behavior. In the latter case, future comparisons might reveal extraordinary plasticity in how the brain forms social bonds and alters behavior in family groups.

Phodopus campbelli detect reduced photoperiod during development but, unlike Phodopus sungorus, retain functional reproductive physiology.

Golden (Mesocricetus auratus) and Siberian (Phodopus sungorus) hamsters are widely used as animal models for seasonal reproduction; but M. auratus shows no developmental delay in short days until after sexual maturity, whereas P. sungorus juveniles delay development in short days. As the photoperiodic response of Phodopus campbelli is not well established, litters of the two Phodopus species were gestated and reared under long days (14 h light:10 h darkness) or short days (10 h light:14 h darkness) until 70 days of age. As expected, under short photoperiod P. sungorus showed reduced body, testes, epididymides, uterus, and ovary weight; antral follicles and corpora lutea were absent and vaginae remained closed. Animals moulted to winter pelage, and low concentrations of each of leptin, testosterone, and prolactin were present in male serum. Phodopus campbelli juveniles also responded to the short photoperiod as measured by reduced body, testes, epididymides, and ovary weight. The summer pelage persisted. However, both sexes of P. campbelli developed functional reproduction under 10 h light:14 h darkness. All females had a patent vagina by 10 weeks; ovaries contained antral follicles and corpora lutea, and uteri were not reduced in weight. In males, the concentrations of testosterone, leptin, and prolactin were not reduced by short photoperiod. Developmental patterns in the three species of hamster, therefore, differ and are not predicted by relatedness or latitude of origin. Other ecological traits, such as predictability of summer rainfall, ambient temperature, and differential responses to social cues might be important.