Cool sex? Hibernation and reproduction overlap in the echidna

Mating in the cold. Prolonged sperm storage provides opportunities for forced copulation by male bats during winter

In a wide range of heterothermic mammals, hibernation interrupts the reproductive cycle by forcing reproductive delays. In hibernating bats with delayed fertilization, an opportunity for sperm competition is enhanced by extending a time-window between copulations and fertilization. In order to achieve greater fertilization success, males are expected to show adaptations for sperm competition by increasing their opportunities for mating over an extended period. We aimed to clarify the physiological and behavioral characteristics of male bats experiencing increased risks of sperm competition. We investigated the characteristics of the reproductive cycle of the little horseshoe bat (Rhinolophus cornutus), and examined whether males retain reproductive physiology related to sexual behavior, and attempt to copulate with females even during the hibernation period. Field observations and histological examinations of the reproductive cycle confirmed that females, having mated in the autumn, store spermatozoa in the uterus during hibernation and give birth in the early summer to just one offspring per year, thus males face a low certainty of successful fertilization. Although their testes regressed rapidly and their testosterone levels were lower during winter than in autumn, males stored motile spermatozoa in their cauda epididymides from autumn throughout the winter. During hibernation, we found that males occasionally aroused from torpor and attempted to mate forcibly with torpid females. Forced copulations appear to increase a male's chances of obtaining a mate while avoiding pre-copulatory female choice. Epididymal sperm storage could be advantageous for males in allowing them to extend their potential mating period even though their testes have regressed. We also found that some hibernating nulliparous females were ready for fertilization in spring after hibernation, whereas few parous females appeared in the same roost. In contrast to males, forced copulations would be maladaptive for females because they cannot opt for higher-quality males while in torpor. Females that have experienced sexual coercion when young may subsequently avoid hibernacula where adult males are present.

Documenting the microbiome diversity and distribution in selected fleas from South Africa with an emphasis on the cat flea, Ctenocephalides f. felis

The factors that influence parasite associated bacterial microbial diversity and the geographic distributions of bacteria are not fully understood. In an effort to gain a deeper understanding of the relationship between the bacterial diversity of Ctenocephalides fleas and host species and the external environment, we conducted a metagenetic analysis of 107 flea samples collected from 8 distinct sampling sites in South Africa. Pooled DNA samples mostly comprising of 2 or 3 individuals sampled from the same host, and belonging to the same genetic cluster, were sequenced using the Ion PGM™ Hi-Q™ Kit and the Ion 316™ Chip v2. Differences were detected in the microbiome compositions between Ctenocephalides felis, Ctenocephalides canis and Ctenocephalides connatus. Although based on a small sample, C. connatus occurring on wildlife harboured a higher bacterial richness when compared to C. felis on domestic animals. Intraspecific differences in the microbial OTU diversity were detected within C. f. felis that occurred on domestic cats and dogs. Different genetic lineages of C. f. felis were similar in microbial compositions but some differences exist in the presence or absence of rare bacteria. Rickettsia and Bartonella OTU's identified in South African cat fleas differ from those identified in the USA and Australia. Intraspecific microbial compositions also differ across geographic sampling sites. Generalized dissimilarity modelling showed that temperature and humidity are potentially important environmental factors explaining the pattern obtained.

Seasonal Expression of Avian and Mammalian Daily Torpor and Hibernation: Not a Simple Summer-Winter Affair†

Daily torpor and hibernation (multiday torpor) are the most efficient means for energy conservation in endothermic birds and mammals and are used by many small species to deal with a number of challenges. These include seasonal adverse environmental conditions and low food/water availability, periods of high energetic demands, but also reduced foraging options because of high predation pressure. Because such challenges differ among regions, habitats and food consumed by animals, the seasonal expression of torpor also varies, but the seasonality of torpor is often not as clear-cut as is commonly assumed and differs between hibernators and daily heterotherms expressing daily torpor exclusively. Hibernation is found in mammals from all three subclasses from the arctic to the tropics, but is known for only one bird. Several hibernators can hibernate for an entire year or express torpor throughout the year (8% of species) and more hibernate from late summer to spring (14%). The most typical hibernation season is the cold season from fall to spring (48%), whereas hibernation is rarely restricted to winter (6%). In hibernators, torpor expression changes significantly with season, with strong seasonality mainly found in the sciurid and cricetid rodents, but seasonality is less pronounced in the marsupials, bats and dormice. Daily torpor is diverse in both mammals and birds, typically is not as seasonal as hibernation and torpor expression does not change significantly with season. Torpor in spring/summer has several selective advantages including: energy and water conservation, facilitation of reproduction or growth during development with limited resources, or minimisation of foraging and thus exposure to predators. When torpor is expressed in spring/summer it is usually not as deep and long as in winter, because of higher ambient temperatures, but also due to seasonal functional plasticity. Unlike many other species, subtropical nectarivorous blossom-bats and desert spiny mice use more frequent and pronounced torpor in summer than in winter, which is related to seasonal availability of nectar or water. Thus, seasonal use of torpor is complex and differs among species and habitats.

Physiological, Behavioral, and Life-History Adaptations to Environmental Fluctuations in the Edible Dormouse

The edible dormouse (Glis glis, formerly Myoxus glis) is a small arboreal mammal inhabiting deciduous forests in Europe. This rodent shows behavioral and physiological adaptations to three types of environmental fluctuations: (i) predictable seasonal variation in climate and food resources (ii) unpredictable year-to-year fluctuation in seed-production by trees and (iii) day-to-day variation in ambient temperature and precipitation. They cope with seasonally fluctuating conditions by seasonal fattening and hibernation. Dormice have adjusted to tree-mast fluctuations, i.e., pulsed resources, by sensing future seed availability in spring, and restricting reproduction to years with at least some seed production by beech and oak trees, which are a crucial food-resource for fast-growing juveniles in fall. Finally, dormice respond to short-term drops in ambient temperature by increased use of daily torpor as well as by huddling in groups of up to 24 conspecifics. These responses to environmental fluctuations strongly interact with each other: Dormice are much more prone to using daily torpor and huddling in non-reproductive years, because active gonads can counteract torpor and energy requirements for reproduction may prevent the sharing of food resources associated with huddling. Accordingly, foraging activity in fall is much more intense in reproductive mast years. Also, depending on their energy reserves, dormice may retreat to underground burrows in the summers of non-reproductive years, causing an extension of the hibernation season to up to 11.4 months. In addition to these interactions, responses to environmental fluctuations are modulated by the progression of life-history stages. With increasing age and diminishing chances of future reproduction, females reproduce with increasing frequency even under suboptimal environmental conditions. Simultaneously, older dormice shorten the hibernation season and phase-advance the emergence from hibernation in spring, apparently to occupy good breeding territories early, despite increased predation risk above ground. All of the above adaptions, i.e., huddling, torpor, hibernation, and reproduction skipping do not merely optimize energy-budgets but also help to balance individual predation risk against reproductive success, which adds another layer of complexity to the ability to make flexible adjustments in this species.

The interrelationship between torpor expression and nest site use of western and eastern pygmy-possums (Cercartetus spp.)

Physiology and behaviour are closely linked, making knowledge of the interaction between species’ energetics and activities important when attempting to understand how animals function in the wild. I examined torpor use by western pygmy-possums (Cercartetus concinnus) and eastern pygmy-possums (C. nanus) in relation to nest site characteristics and movement patterns. In coastal mallee heath in winter, C. concinnus nested beneath leaf litter at the base of dead Banksia ornata, where they employed torpor on 69% of observed days. In warm temperate sclerophyll forest, C. nanus nested in tree hollows of Eucalyptus spp. and used torpor on 64% of days in winter and 10% in summer. Torpor was used in nest sites that were buffered from outside temperature extremes. Both species frequently reused nest sites and while C. nanus was more likely to employ torpor in a previously used site, site familiarity did not influence torpor use for C. concinnus. Additionally, C. nanus was more likely to use torpor in hollows with a higher relative thickness in both seasons. No relationship was found between range size and the number of tracking days or capture body mass, though sample sizes were small. I suggest that the thermal attributes of nest sites influence torpor use for both species and this is likely vital for maintaining a positive energy balance, stressing the importance of preserving habitat with ample potential nest sites for conservation management.

Thermal physiology and activity in relation to reproductive status and sex in a free-ranging semelparous marsupial

In a changing climate, southern hemisphere mammals are predicted to face rising temperatures and aridity, resulting in food and water shortages, which may further challenge already constrained energetic demands. Especially semelparous mammals may be threatened because survival of the entire population depends on the success of a single breeding event. One of these species, the yellow-footed antechinus, Antechinus flavipes, a small, heterothermic marsupial mammal, commences reproduction during winter, when insect prey is limited and energetic constraints are high. We examined the inter-relations between thermal and foraging biology of free-ranging A. flavipes and examined whether they use torpor for energy conservation, despite the fact that reproduction and torpor are considered to be incompatible for many mammals. Females used torpor during the reproductive season, but patterns changed with reproductive status. Prior to breeding, females used frequent (86% of days), deep and long torpor that was more pronounced than any other reproductive group, including pre-mating males (64% of days). Pregnant females continued to use torpor, albeit torpor was less frequent (28% of days) and significantly shorter and shallower than before breeding. Parturient and lactating females did not express torpor. During the mating period, males reduced torpor use (24% of days). Pre-reproductive females and pre-mating males were the least active and may use torpor to minimize predator exposure and enhance fat deposition in anticipation of the energetic demands associated with impending mating, gestation and lactation. Reproductive females were most active and likely foraged and fed to promote growth and development of young. Our data show that A. flavipes are balancing energetic demands during the reproductive season by modifying torpor and activity patterns. As the timing of reproduction is fixed for this genus, it is probable that climate change will render these behavioural and physiological adaptations as inadequate and threaten this and other semelparous species.

Challenges associated with the development and transfer of assisted breeding technology in marsupials and monotremes: lessons from the koala, wombat and short-beaked echidna

This reflective review describes how a research model, which was originally established for the successful AI of the koala (Phascolarctos cinereus), is currently being developed and extended to the wombat (Lasiorhinus latifrons and Vombatus ursinus) and short-beaked echidna (Tachyglossus aculeatus). The research model centres around the establishment of an AI program and involves: (1) semen collection, evaluation and preservation, requiring an understanding of male reproductive physiology and gamete biology; (2) timing of insemination, based on a knowledge of oestrous cycle and gestation physiology and oestrous behaviour; and (3) the appropriate placement of semen, which relies on an accurate description of female reproductive anatomy. Published and unpublished studies of assisted breeding technology (ABT) development in all three species of Australian mammals reported in this review (koala, wombat and short-beaked echidna) clearly demonstrate the importance of recognising species-specific variation in reproductive biology. Even in closely related species, such as the koala and wombat, subtle differences in reproductive physiology can hinder the transfer of ABT across species. Significant progress in marsupial and monotreme ABT will also require adequate access to captive wildlife colonies (zoos, university collections and private partners) in sufficient numbers in order to conduct quality science.

Flood-induced multiday torpor in golden spiny mice (Acomys russatus)

Mammalian and avian torpor is widely viewed as an adaptation for survival of cold winters. However, in recent years it has been established that torpor can also be expressed in summer and that the functions of torpor are manyfold, including survival of adverse environmental events such as fires, storms, heat waves and droughts. Here we provide the first evidence on (1) torpor induction via an accidental flooding event in mammals (in captivity) and (2) expression of multiday torpor by spiny mice, lasting >7 times as long as usually observed for this desert rodent. Our data suggest yet another function of mammalian torpor, as a response to flood, in addition to many other adverse environmental events, and not just in response to cold.

More functions of torpor and their roles in a changing world

Increased winter survival by reducing energy expenditure in adult animals is often viewed as the primary function of torpor. However, torpor has many other functions that ultimately increase the survival of heterothermic mammals and birds. In this review, we summarize new findings revealing that animals use torpor to cope with the conditions during and after natural disasters, including fires, storms, and heat waves. Furthermore, we suggest that torpor, which also prolongs longevity and was likely crucial for survival of mammals during the time of the dinosaur extinctions, will be advantageous in a changing world. Climate change is assumed to lead to an increase in the occurrence and intensity of climatic disasters, such as those listed above and also abnormal floods, droughts, and extreme temperatures. The opportunistic use of torpor, found in many heterothermic species, will likely enhance survival of these challenges, because these species can reduce energy and foraging requirements. However, many strictly seasonal hibernators will likely face the negative consequences of the predicted increase in temperature, such as range contraction. Overall, available data suggest that opportunistic heterotherms with their flexible energy requirements have an adaptive advantage over homeotherms in response to unpredictable conditions.

Frozen embryos? Torpor during pregnancy in the Tasmanian short-beaked echidna Tachyglossus aculeatus setosus

We studied the interaction between torpor and reproduction in free-ranging female Tasmanian echidnas using a combination of techniques including urogenital smears, hormone analysis, ultrasonography, external temperature loggers and camera traps. Male echidnas initiated mating activity by locating hibernating females. All females that mated or were disturbed by males prior to July 27 re-entered hibernation, including many that were pregnant. Pregnant females only entered hibernation in early pregnancy when plasma progesterone concentrations were about twice basal and progesterone then remained constant during torpor. By re-entering hibernation pregnant females extended their gestation period and delayed egg-laying. Progesterone peaked 4-6days before egg-laying, then dropped rapidly.

Evaluation of the bacterial microbiome of two flea species using different DNA-isolation techniques provides insights into flea host ecology

Fleas (Siphonaptera) are ubiquitous blood-sucking pests of animals worldwide and are vectors of zoonotic bacteria such as Rickettsia and Bartonella. We performed Ion Torrent PGM amplicon sequencing for the bacterial 16S rRNA gene to compare the microbiome of the ubiquitous cat flea (Ctenocephalides f. felis) and the host-specific echidna stickfast flea (Echidnophaga a. ambulans) and evaluated potential bias produced during common genomic DNA-isolation methods. We demonstrated significant differences in the bacterial community diversity between the two flea species but not between protocols combining surface sterilisation with whole flea homogenisation or exoskeleton retention. Both flea species were dominated by obligate intracellular endosymbiont Wolbachia, and the echidna stickfast fleas possessed the endosymbiont Cardinium. Cat fleas that were not surface sterilised showed presence of Candidatus 'Rickettsia senegalensis' DNA, the first report of its presence in Australia. In the case of Rickettsia, we show that sequencing depth of 50 000 was required for comparable sensitivity with Rickettsia qPCR. Low-abundance bacterial genera are suggested to reflect host ecology. The deep-sequencing approach demonstrates feasibility of pathogen detection with simultaneous quantitative analysis and evaluation of the inter-relationship of microbes within vectors.

Advances in the captive breeding and reproductive biology of the short-beaked echidna (Tachyglossus aculeatus)

Captive breeding of the short-beaked echidna (Tachyglossus aculeatus) has proven a difficult challenge; as recently as 2009, there were fewer than 10 echidnas born in captivity. We present observations of captive reproductive behaviour following video surveillance and measurements of body temperature collected from six captive female echidnas over a six-year period. In the first series of observations (2009–10) we examined the efficacy of artificial burrow boxes as possible aids for reproductive success. Females with access to burrow boxes had significantly higher levels of reproductive activity (P = 0.001), there was coincidental improvement in the production of eggs or pouch young (two eggs, one unhatched and one offspring). During 2009–10, a range of reproductive behaviours (courtship, copulation and postcopulation) were documented and analysed, as were new observations of oestrous cycle activity. Female body temperature was characteristically stable during egg incubation during this study and has the potential to be used as a tool for the assessment of reproductive status. Following initial observations, burrow boxes and infrared lamps were implemented as standard husbandry in our echidna breeding facility and the effects on reproductive success were monitored, albeit less intensively, for a further four years (2011–14). Although no direct causal effect could be ascribed, the use of burrow boxes and heat lamps coincided with a total of 13 young being born to four females in the last four years (2011–14). These female echidnas were found to be receptive at intervals throughout the breeding season, both before and after presumed incubation phases, suggesting that captive animals exhibit polyoestry. In 2012 and 2014, the same female showed evidence of producing two young from one breeding event.

Effects of reproductive status and high ambient temperatures on the body temperature of a free-ranging basoendotherm

Tenrecs (Order Afrosoricida) exhibit some of the lowest body temperatures (T b) of any eutherian mammal. They also have a high level of variability in both active and resting T bs and, at least in cool temperatures in captivity, frequently employ both short- and long-term torpor. The use of heterothermy by captive animals is, however, generally reduced during gestation and lactation. We present data long-term T b recordings collected from free-ranging S. setosus over the course of two reproductive seasons. In general, reproductive females had slightly higher (~32 °C) and less variable T b, whereas non-reproductive females and males showed both a higher propensity for torpor as well as lower (~30.5 °C) and more variable rest-phase T bs. Torpor expression defined using traditional means (using a threshold or cut-off T b) was much lower than predicted based on the high degree of heterothermy in captive tenrecs. However, torpor defined in this manner is likely to be underestimated in habitats where ambient temperature is close to T b. Our results caution against inferring metabolic states from T b alone and lend support to the recent call to define torpor in free-ranging animals based on mechanistic and not descriptive variables. In addition, lower variability in T b observed during gestation and lactation confirms that homeothermy is essential for reproduction in this species and probably for basoendothermic mammals in general. The relatively low costs of maintaining homeothermy in a sub-tropical environment might help shed light on how homeothermy could have evolved incrementally from an ancestral heterothermic condition.

Timing is the only thing: reproduction in female yellow ground squirrels (Spermophilus fulvus)

Based on 4-year field observations of yellow ground squirrels (Spermophilus fulvus (Lichtenstein, 1823)), we determined whether female reproductive effort, annual reproductive success, and survival were dependent on age, body condition, time of emergence from hibernation, and previous reproduction. The probability of weaning a litter did not vary with female age, body condition, time of emergence, or previous reproduction. Litter size, litter mass, and offspring survival did not vary with age, whereas individual offspring mass was lower in yearlings than in older females. Body condition upon emergence had no effect on litter size, litter mass, offspring mass, and survival. Reproduction did not influence female survival, physical condition upon emergence next spring, or subsequent reproductive efforts. The only factor that affected the extent of reproductive effort and offspring survival was the date of emergence: the later a female emerged, the lower the total and mean offspring mass, and fewer offspring survived. The modulation of reproduction in female S. fulvus by only the timing of vernal emergence and independent of other individual characteristics can be explained by the high costs of missed reproductive opportunity because of short longevity combined with low costs of reproduction when resources are abundant enough to meet both somatic and reproductive needs.

Torpor during reproduction in mammals and birds: dealing with an energetic conundrum

Torpor and reproduction in mammals and birds are widely viewed as mutually exclusive processes because of opposing energetic and hormonal demands. However, the reported number of heterothermic species that express torpor during reproduction is ever increasing, to some extent because of recent work on free-ranging animals. We summarize current knowledge about those heterothermic mammals that do not express torpor during reproduction and, in contrast, examine those heterothermic birds and mammals that do use torpor during reproduction. Incompatibility between torpor and reproduction occurs mainly in high-latitude sciurid and cricetid rodents, which live in strongly seasonal, but predictably productive habitats in summer. In contrast, torpor during incubation, brooding, pregnancy, or lactation occurs in nightjars, hummingbirds, echidnas, several marsupials, tenrecs, hedgehogs, bats, carnivores, mouse lemurs, and dormice. Animals that enter torpor during reproduction often are found in unpredictable habitats, in which seasonal availability of food can be cut short by changes in weather, or are species that reproduce fully or partially during winter. Moreover, animals that use torpor during the reproductive period have relatively low reproductive costs, are largely insectivorous, carnivorous, or nectarivorous, and thus rely on food that can be unpredictable or strongly seasonal. These species with relatively unpredictable food supplies must gain an advantage by using torpor during reproduction because the main cost is an extension of the reproductive period; the benefit is increased survival of parent and offspring, and thus fitness.

Observations of breeding behaviour and possible infanticide in a wild population of Tasmanian echidnas (Tachyglossus aculeatus setosus)

We describe field observations of Tasmanian echidna behaviour, including possible infanticide, where males damaged and entered nursery burrows. We also present the second report of a female producing a second offspring within a single reproductive season after the loss of her first young at an early stage.

Did postglacial sea-level changes initiate the evolutionary divergence of a Tasmanian endemic raptor from its mainland relative?

Populations on continental islands are often distinguishable from mainland conspecifics with respect to body size, appearance, behaviour or life history, and this is often congruent with genetic patterns. It is commonly assumed that such differences developed following the complete isolation of populations by sea-level rise following the Last Glacial Maximum (LGM). However, population divergence may predate the LGM, or marine dispersal and colonization of islands may have occurred more recently; in both cases, populations may have also diverged despite ongoing gene flow. Here, we test these alternative hypotheses for the divergence between wedge-tailed eagles from mainland Australia (Aquila audax audax) and the threatened Tasmanian subspecies (Aquila audax fleayi), based on variation at 20 microsatellite loci and mtDNA. Coalescent analyses indicate that population divergence appreciably postdates the severance of terrestrial habitat continuity and occurred without any subsequent gene flow. We infer a recent colonization of Tasmania by marine dispersal and cannot discount founder effects as the cause of differences in body size and life history. We call into question the general assumption of post-LGM marine transgression as the initiator of divergence of terrestrial lineages on continental islands and adjacent mainland, and highlight the range of alternative scenarios that should be considered.

A functional nexus between photoperiod acclimation, torpor expression and somatic fatty acid composition in a heterothermic mammal

The seasonal changes in thermal physiology and torpor expression of many heterothermic mammals are controlled by photoperiod. As function at low body temperatures during torpor requires changes of tissue lipid composition, we tested for the first time whether and how fatty acids are affected by photoperiod acclimation in hamsters, Phodopus sungorus, a strongly photoperiodic species. We also examined changes in fatty acid composition in relation to those in morphology and thermal biology. Hamsters in short photoperiod had smaller reproductive organs and most had a reduced body mass in comparison to those in long photoperiod. Pelage colour of hamsters under short photoperiod was almost white while that of long photoperiod hamsters was grey-brown and black. Short photoperiod acclimation resulted in regular (28% of days) torpor use, whereas all hamsters in long photoperiod remained normothermic. The composition of total fatty acids differed between acclimation groups for brown adipose tissue (5 of 8 fatty acids), heart muscle (4 of 7 fatty acids) and leg muscle (3 of 11 fatty acids). Importantly, 54% of all fatty acids detected were correlated (r² = 0.60 to 0.87) with the minimum surface temperature of individuals, but the responses of tissues differed. While some of the compositional changes of fatty acids were consistent with a ‘homeoviscous’ response, this was not the case for all, including the sums of saturated and unsaturated fatty acids, which did not differ between acclimation groups. Our data identify a possible nexus between photoperiod acclimation, morphology, reproductive biology, thermal biology and fatty acid composition. They suggest that some of the changes in thermal physiology are linked to the composition of tissue and organ fatty acids.

The influence of reproductive hormones on the torpor patterns of the marsupial Sminthopsis macroura: bet-hedging in an unpredictable environment

Seasonal cycles of reproduction are common in many mammals and these are combined with the necessary energy budgeting for thermoregulatory challenges. Many mammals meet the challenge of changing environmental temperatures in winter by using torpor, a controlled reduction in body temperature and metabolic rate. We aimed to determine the effects of photoperiod and reproductive hormones on the seasonal cycles of reproduction and torpor use in a marsupial that commences reproduction in winter, the stripe-faced dunnart, Sminthopsis macroura. Males and females were placed under LD 14:10 and natural reproductive hormones blocked by either flutamide (males) or mifepristone (females) or tamoxifen (females). Reproductive parameters, metabolic rate and torpor variables were determined. The same animals were then placed under LD 10:14 and given testosterone (males) or progesterone (females) or oestrogen (females). Reproductive parameters, metabolic rate and torpor variables were measured. Body mass and tail widths (fattening indicator) in males were significantly affected by testosterone, and the effects were reversed by hormone blockers. Reproductive parameters were unaffected. Resting metabolic rate and ability to use torpor were not affected by treatment in males, however torpor characteristics, especially torpor bout duration, were affected by presence of testosterone in males. In females, body mass was unaffected by hormone presence, although tail widths were affected. Disruption of reproductive cycles occurred with hormone blockers in females, however, resting metabolic rate was not affected, and only presence of progesterone affected torpor characteristics in females. Our results differ from those found for rodents, where presence of testosterone abolishes the use of torpor in males, and oestrogen inhibits torpor use in females. Our study suggests that, in this mammal, metabolic responses to the presence or absence of reproductive hormones differs between males and females, and there is no absolute endocrinologically-driven reproductive season demarcated from the torpor season.

The tradeoff between torpor use and reproduction in little brown bats (Myotis lucifugus)

In mammals, reproduction, especially for females is energetically demanding. Therefore, during the reproductive period females could potentially adjust patterns of thermoregulation and foraging in concert to minimise the energetic constraints associated with pregnancy and lactation. We assessed the influence of pregnancy, lactation, and post-lactation on torpor use and foraging behaviour by female little brown bats, Myotis lucifugus. We measured thermoregulation by recording skin temperature and foraging by tracking bats which carried temperature-sensitive radio-tags. We found that individuals, regardless of reproductive condition, used torpor, but the patterns of torpor use varied significantly between reproductive (pregnant and lactating) females and post-lactating females. As we predicted, reproductive females entered torpor for shorter bouts than post-lactating females. Although all females used torpor frequently, pregnant females spent less time in torpor, and maintained higher skin temperatures than either lactating or post-lactating females. This result suggests that delayed offspring development which has been associated with torpor use during pregnancy, may pose a higher risk to an individual's reproductive success than reduced milk production during lactation. Conversely, foraging behaviour of radio-tagged bats did not vary with reproductive condition, suggesting that even short, shallow bouts of torpor produce substantial energy savings, likely obviating the need to spend more time foraging. Our data clearly show that torpor use and reproduction are not mutually exclusive and that torpor use (no matter how short or shallow) is an important means of balancing the costs of reproduction for M. lucifugus.

Does leptin signal adiposity in the egg-laying mammal, Tachyglossus aculeatus?

Leptin is a peptide hormone best known for its role in feedback regulation of adiposity in eutherian mammals. Normally an increase in adipose tissue mass leads to an increase in circulating leptin which increases energy expenditure and limits food intake, but in hibernating eutherian mammals this relationship may change to allow prehibernatory fattening. The echidna (Tachyglossus aculeatus) is a monotreme mammal which accumulates significant fat reserves before entering hibernation, and mates immediately at the end of hibernation. We hypothesised that echidnas would show a strong relationship between body mass and plasma leptin for most of the year which would change during the pre-hibernatory period. We measured plasma leptin and body mass in free-ranging echidnas over several reproductive and hibernation cycles. There were significant seasonal variations in plasma leptin in both sexes, with the highest levels occurring in hibernation and in mating females. The lowest levels were found in males when they were foraging maximally after the reproductive period. We used mass%, body mass at the time of sampling as a percentage of long term mean mass, as a proxy for adiposity. There was a weak negative relationship between mass% and plasma leptin, from which we infer a weak negative relationship between adiposity and plasma leptin as has been found in reptiles and birds, rather than the strong positive relationship found in other mammals.

Chemical composition of odorous secretions in the Tasmanian short-beaked echidna (Tachyglossus aculeatus setosus)

The short-beaked echidna is believed to use olfactory cues from a cloacal scent gland to attract and locate mates during the breeding season. We investigated the chemical composition of echidna secretions, including cloacal swabs and solid, "waxy" exudates from the cloaca and spurs. Scent samples from 37 individuals were collected over a 1-year period and analyzed using a range of different analytical techniques. A total of 186 compounds were identified, including volatile carboxylic acids, aldehydes, ketones, fatty acids, methyl esters, ethyl esters, terpenes, nitrogen- and sulphur-containing compounds, alcohols, and aromatics. Long chain and very long chain monounsaturated fatty acids, sterols, and sterol esters were identified as the major constituents of solid exudates, some of which have not previously been described from any animal skin gland. There was a high degree of composition overlap between male and female cloaca swabs; however, there is significant variation, which could mediate echidna mating behavior. Many of the volatile and nonvolatile chemicals detected are used for communication in other species, suggesting that chemical signals have important and diverse functions in echidna social interactions.

Cool running: locomotor performance at low body temperature in mammals

Mammalian torpor saves enormous amounts of energy, but a widely assumed cost of torpor is immobility and therefore vulnerability to predators. Contrary to this assumption, some small marsupial mammals in the wild move while torpid at low body temperatures to basking sites, thereby minimizing energy expenditure during arousal. Hence, we quantified how mammalian locomotor performance is affected by body temperature. The three small marsupial species tested, known to use torpor and basking in the wild, could move while torpid at body temperatures as low as 14.8-17.9°C. Speed was a sigmoid function of body temperature, but body temperature effects on running speed were greater than those in an ectothermic lizard used for comparison. We provide the first quantitative data of movement at low body temperature in mammals, which have survival implications for wild heterothermic mammals, as directional movement at low body temperature permits both basking and predator avoidance.

Maternal care in the Tasmanian echidna (Tachyglossus aculeatus setosus)

Parental care is central to the differences in reproductive behaviour and energy expenditure between males and females, and it is therefore crucial for understanding animal mating systems. We investigated post-gestation maternal care in a wild population of short-beaked echidnas (Tachyglossus aculeatus) in the Tasmanian midlands using a combination of external temperature loggers and motion-triggered infrared cameras. For the first few weeks of early lactation mothers do not leave their nursery burrow, which they keep at a stable and warm temperature, resulting in a greater rate of maternal mass loss during the period of maternal burrow confinement than during hibernation. However, after lactating mothers recommence feeding, they raise a young to ~1.5 kg on a diet of their milk while increasing their own body mass by a similar amount. Weaning in our population appears not to be abrupt as there is a period where young echidnas begin exploratory foraging while their mother is still lactating. After young are weaned and abandon the nursery burrow, there appear to be no further associations between mothers and young despite young echidnas remaining within their mother’s home range for the first 12 months of their life. Female echidnas time reproductive events with increases in ecosystem productivity, so that young are weaned at a time of maximum food abundance.

Historical male-mediated introgression in horseshoe bats revealed by multilocus DNA sequence data

Instances of hybridization between mammalian taxa in the wild are rarely documented. To test for introgression between sibling species of horseshoe bat (Rhinolophus yunanensis and R. pearsoni) and two subspecies of the latter (R. p. pearsoni and R. p. chinensis), we sequenced two mtDNA and two ncDNA markers in individuals sampled from multiple localities within their overlapping ranges. The interspecific mtDNA gene tree corresponded to the expected taxonomic divisions, and coalescent-based analyses suggested divergence occurred around 4 MYA. However, these relationships strongly conflicted with those recovered from two independent nuclear gene trees, in which R. yunanensis clustered with R. p. pearsoni to the exclusion of R. p. chinensis. This geographically widespread discordance is best explained by large-scale historical introgression of ncDNA from R. yunanensis to R. pearsoni by male-mediated exchange in mixed species colonies during Pleistocene glacial periods, when ranges may have contracted and overlapped more than at present. Further species tree-gene tree conflicts were detected between R. p. pearsoni and R. p. chinensis, also indicating past and/or current introgression in their overlapping regions. However, here the patterns point to asymmetric mtDNA introgression without ncDNA introgression. Analyses of coalescence times indicate this exchange has occurred subsequent to the divergence of these subspecies from their common ancestor. Our work highlights the importance of using multiple data sets for reconstructing phylogeographic histories and resolving taxonomic relationships.

Thermoregulation in monotremes: riddles in a mosaic

The three extant genera of the Monotremata have evolved, probably from a pre-Cretaceous Gondwanan origin, independently of the Theria to display a variety of ancestral and derived features. A comparison of their thermoregulation reveals a diversity of physiology that might represent both plesiomorphic and apomorphic elements within this mosaic. In the tachyglossids, the echidnas Tachyglossus and Zaglossus, body temperature is often labile, rising as a result of activity and allowed to decline during inactivity. This daily heterothermy, which is not necessarily torpor, may combine with typical mammalian hibernation to provide substantial energy economy in a wide variety of often unproductive habitats. Only when incubating do free-ranging echidnas display classic mammalian thermoregulation, the facultative nature of which suggests echidna-like physiology as an example of a protoendothermic stage in the evolution of endothermy. Similarly, physiological response to heat in Tachyglossus, at least, may be plesiomorphic, relying on the cyclic loss of heat stored during activity. Tachyglossids neither exhibit a panting response nor spread saliva to facilitate evaporative cooling and Tachyglossus, though not Zaglossus, lacks functional sweat glands. By contrast, the only extant ornithorhynchid, the platypus Ornithorhynchus, does not utilise heterothermy of any kind and maintains its body temperature more tightly than several semiaquatic eutherians. Although not necessarily required, it responds to heat via sweating, but not panting or saliva spreading. The classic nature of ornithorhynchid thermoregulation stands in marked contrast to the more diverse thermoregulatory responses shown by the tachyglossids, making it difficult to determine which aspects of monotreme thermoregulation are plesiomorphic and which are apomorphic.

Reproductive strategies of the short-beaked echidna - a review with new data from a long-term study on the Tasmanian subspecies (Tachyglossus aculeatus setosus)

The short-beaked echidna is the most widely distributed endemic Australian mammal, and echidnas from different geographic areas differ so much in appearance that they have been assigned to several subspecies. In this paper, we present data obtained from free-ranging echidnas in southern Tasmania, and compare this with studies from other parts of Australia. In Tasmania mating occurs between early June and mid-September, and throughout Australia the normal breeding season lies within these limits. In echidnas from the more easterly parts of Australia reproduction closely follows hibernation, with Tasmanian echidnas showing a significant overlap between hibernation and reproduction. There is intense competition between males, and female echidnas from Tasmania show multiple matings. There are significant differences between echidnas from different areas of Australia in the use of nursery burrows and maternal care. One of the most dramatic differences is in duration of lactation: echidnas from Kangaroo Island wean the young at 204–210 days, but in Tasmania weaning occurs at 139–152 days, even though the masses of the young at weaning are comparable.