Non-reproductive Females Research Articles

Effects of season and social status on gonadal function in social Natal mole-rats

The reproductive cycle of mammals can be inhibited by 2 factors, seasonal breeding and dominance control, both potentially important in mole-rats. The gonads and gonadal steroids of dominant (reproductive) and subordinate (nonreproductive) Natal mole-rats (Cryptomys hottentotus natalensis) were investigated to determine the effects of season and social status on reproduction within natal colonies. We found no seasonal differences in concentrations of gonadal steroids of male or female mole-rats. Similarly, the gonadal histology and volume showed no seasonal differences. These results, together with the presence of fetuses, confirm the potential for breeding throughout the year. Reproductive and nonreproductive mole-rats display comparable testosterone and estrogen concentrations in males and females, respectively. Follicular development and the presence and number of sperm in nonreproductive animals suggest that the reproductive quiescence in nonreproductive animals is likely to result from behavioral interference of dominant animals or incest avoidance (or both). Urinary progesterone concentrations of reproductive females were significantly higher than those of nonreproductive females. Although follicular development in nonreproductive females proceeds to the level of Graafian follicles, the number of these follicles present in nonreproductive females was significantly less than that in reproductive females. The reproductive physiology of the Natal mole-rat compares with other loosely social mole-rat species inhabiting mesic areas.

Variation in the abundance of ectoparasitic mites of flat-headed bats

We investigated the ectoparasitic mite loads (Macronyssus: Macronyssidae: Acarina) on 2 species of flat-headed bats, Tylonycteris pachypus and T. robustula (Mammalia: Chiroptera: Vespertilionidae) in 2 counties of Guangxi Province, southern China, from 2002 to 2005. In Longzhou County both species of bat occur sympatrically, but only T. pachypus occurs in Ningming County. Individuals of the smaller species (T. pachypus) harbored significantly more mites than did those of T. robustula. In both species males harbored more mites than nonreproductive females, pregnant females had more mites than lactating and nonreproductive females, and juveniles harbored more mites than adults. Mite load on both species of bats showed significant seasonal variation, declining from spring to winter. No correlation was found between mite load and size of the host colony. We discuss our findings in relation to the ecology and biology of both hosts and parasites.

Evolution of viviparity and uterine angiogenesis: vascular endothelial growth factor (VEGF) in oviparous and viviparous skinks

During pregnancy, uterine vasculature of live-bearing lizards proliferates to support embryonic growth and development. Vascular endothelial growth factor (VEGF) is the most potent of a suite of growth factors responsible for uterine vascularization in mammals. We have sequenced VEGF mRNA transcripts expressed in the uterus of oviparous and viviparous Australian skinks, and compared uterine VEGF expression in nonreproductive and late-reproductive Saiphos equalis, a fossorial viviparous skink. VEGF sequences differed between phylogenetic groups of skinks, rather than oviparous and viviparous skinks. Two transcripts were identified in the uterus of each species that had the same splice sites as human VEGF(165) and VEGF(189). A third transcript, found only in uterine and testis tissue from S. equalis, had the same splice sites as human VEGF(111). This is the first natural expression of VEGF(111), previously found only in human cultured cells subjected to environmental stress. All the three VEGF transcripts identified showed higher expression in uterus from late-reproductive S. equalis than nonreproductive females. The different angiogenic properties of VEGF transcripts provide a mechanism that may produce the variety of placental complexities observed in viviparous skinks. The presence of VEGF(111) in S. equalis may be an opportunity to investigate the function of this unique transcript in a whole animal system.

More than one inseminated female in colonies of the independent-founding wasp Mischocyttarus cassununga von Ihering (Hymenoptera, Vespidae)

In the primitively eusocial wasps, especially Polistini and Mischocyttarini tribes, the physiological condition of each individual is strongly associated with its dominance status in the colonial hierarchy. As a rule, in independent-founding wasps, female wasps are all morphologically alike, and their role is apparently quite flexible even as adults. However, some studies have shown that differences in body size can exist between reproductive and non-reproductive females. Thus, the present study aimed at detecting differences between reproductive (inseminated) and non-reproductive (uninseminated) individuals based on morphological and physiological parameters. We tape-recorded the daily behavioural repertory of six colonies of Mischocyttarus cassununga for determining the hierarchical dominance in the field, and then collected these colonies (in different cycle stages) for measuring 13 set characters, and assessing the physiological condition of each individual by inspecting their fat bodies and ovaries. Our results revealed that inseminated and uninseminated females are not significantly different in relation to body size, in spite of first group shows higher average than second in almost all measured parts. The physiological evaluation of each individual demonstrated more than one inseminated female per colony during all stages of the colony cycle, suggesting a strategic condition of this species against difficulties (predation and parasitism of the colony) in nature.

Induced ovulation mimics the time-table of natural development in the stripe-faced dunnart, Sminthopsis macroura and results in the birth of fertile young

Induced ovulation maximizes captive breeding success, increasing productivity and facilitating the contribution of otherwise infertile animals to the genetic pool. In marsupials, induced ovulation to produce fertile young is unknown. Here we present an induction protocol efficient in inducing non-cycling and non-reproductive females to cycle, mate, ovulate, and conceive. Ovulation was induced in Sminthopsis macroura using an initial injection of 0.06 IU equine serum gonadotropin (eSG)/g (time 0), followed on day 4 by 0.04 IU eSG/g. Using this induction regime, the timing of follicular and embryonic development mimics natural cycles and results in the birth of viable, fertile young. Response to induction is not significantly affected by animal age, making this protocol an effective conservation tool. We have established a time-table of development following induction, providing a source of precisely timed research material. This is the first induced ovulation protocol in any marsupial to result in demonstrated fertile offspring and to allow the reliable collection of known-age samples during both the follicular phase and the gestation period.

A histological investigation of the occurrence of non‐reproductive female bluefin tuna Thunnus thynnus in the Mediterranean Sea

The presence of non-reproductive Atlantic bluefin tuna Thunnus thynnus females in the Mediterranean Sea was investigated through histological analysis of the gonads. Three hundred and twenty-six ovary samples were collected from adults captured at different locations in the Mediterranean Sea during the reproductive seasons between 1998 and 2008. Only three specimens were considered to be in a non-reproductive state: two of them were in a reabsorbing state showing ovaries with early vitellogenic oocytes and extensive alpha and beta atresia of vitellogenic follicles; the third showed gonads with perinucleolar oocytes and was considered to be in a resting state. The low occurrence of non-reproductive individuals found in this study makes it unlikely that non-reproductive individuals aggregate with reproductive ones during their migration towards spawning grounds. Further research is suggested in order to investigate the potential presence of non-reproductive individuals on non-spawning grounds during the reproductive season.

Spatial and temporal patterns of roost use by western long-eared bats (Myotis evotis)

We investigated roost use by western long-eared bats (Myotis evotis), including roost fidelity, movement between roosts and the size of roosting home-ranges. We expected reproductive females, especially lactating females, to exhibit higher roost fidelity and to move shorter distances between roosts than males or nonreproductive females. Individuals generally switched roosts every 1 or 2 d. Despite their low roost fidelity, individuals occupied small roosting home-ranges (<2 ha), demonstrating fidelity to a roosting area. Roost fidelity, distances moved between roosts and roosting home-range sizes were not associated with reproductive class or reproductive period, possibly indicating that any energetic cost of roost switching is trivial in the energy budget of M. evotis, or that the advantages of roost switching outweigh any energetic cost.

Seasonal Plasticity of Auditory Saccular Sensitivity in the Vocal Plainfin Midshipman Fish,Porichthys notatus

The plainfin midshipman fish, Porichthys notatus, is a seasonally breeding species of marine teleost fish that generates acoustic signals for intraspecific social and reproductive-related communication. Female midshipman use the inner ear saccule as the main acoustic endorgan for hearing to detect and locate vocalizing males that produce multiharmonic advertisement calls during the breeding season. Previous work showed that the frequency sensitivity of midshipman auditory saccular afferents changed seasonally with female reproductive state such that summer reproductive females became better suited than winter nonreproductive females to encode the dominant higher harmonics of the male advertisement calls. The focus of this study was to test the hypothesis that seasonal reproductive-dependent changes in saccular afferent tuning is paralleled by similar changes in saccular sensitivity at the level of the hair-cell receptor. Here, I examined the evoked response properties of midshipman saccular hair cells from winter nonreproductive and summer reproductive females to determine if reproductive state affects the frequency response and threshold of the saccule to behaviorally relevant single tone stimuli. Saccular potentials were recorded from populations of hair cells in vivo while sound was presented by an underwater speaker. Results indicate that saccular hair cells from reproductive females had thresholds that were approximately 8 to 13 dB lower than nonreproductive females across a broad range of frequencies that included the dominant higher harmonic components and the fundamental frequency of the male's advertisement call. These seasonal-reproductive-dependent changes in thresholds varied differentially across the three (rostral, middle, and caudal) regions of the saccule. Such reproductive-dependent changes in saccule sensitivity may represent an adaptive plasticity of the midshipman auditory sense to enhance mate detection, recognition, and localization during the breeding season.

Oxytocin-induced elevation of ADP-ribosyl cyclase activity, cyclic ADP-riboseor Ca 2+ concentrations is involved in autoregulation of oxytocin secretionin the hypothalamus and posterior pituitary in male mice

Locally released oxytocin (OT) activates OT receptors (2.1:OXY:1:OT:) in neighboring neurons in the hypothalamus and their terminals in the posterior pituitary, resulting in further OT release, best known in autoregulation occurring during labor or milk ejection in reproductive females. OT also plays a critical role in social behavior of non-reproductive females and even in males in mammals from rodents to humans. Social behavior is disrupted when elevation of free intracellular Ca 2+ concentration ([Ca 2+] i) and OT secretion are reduced in male and female CD38 knockout mice. Therefore, it is interesting to investigate whether ADP-ribosyl cyclase-dependent signaling is involved in OT-induced OT release for social recognition in males, independent from female reproduction, and to determine its molecular mechanism. Here, we report that ADP-ribosyl cyclase activity was increased by OT in crude membrane preparations of the hypothalamus and posterior pituitary in male mice, and that OT elicited an increase in [Ca 2+] i in the isolated terminals over a period of 5 min. The increases in cyclase and [Ca 2+] i were partially inhibited by nonspecific protein kinase inhibitors and a protein kinase C specific inhibitor, calphostin C. Subsequently, OT-induced OT release was also inhibited by calphostin C to levels inhibited by vasotocin, an OT receptor antagonist, and 8-bromo-cADP-ribose. These results demonstrate that OT receptors are functionally coupled to membrane-bound ADP-ribosyl cyclase and/or CD38 and suggest that cADPR-mediated intracellular calcium signaling is involved in autoregulation of OT release, which is sensitive to protein kinase C, in the hypothalamus and neurohypophysis in male mice.

Living on the edge: roads and edge effects on small mammal populations

1. Roads may affect wildlife populations through habitat loss and disturbances, as they create an abrupt linear edge, increasing the proportion of edge exposed to a different habitat. Three types of edge effects have been recognized: abiotic, direct biotic, and indirect biotic. 2. We explored the direct biotic edge effects of 3- to 4-m wide roads, and also a previously unrecognized type of edge effect: social. We live-trapped two threatened endemic rodents from Cozumel Island (Oryzomys couesi cozumelae and Reithrodontomys spectabilis) in 16 plots delimited by roads on two sides, to compare edge effects between two adjacent edges (corners), single-edge and interior forest, on life history and social variables. 3. No significant edge effects were observed on the life-history variables, with the exception of differences in body condition between males and females of O. c. cozumelae near edges. Both species showed significant and contrasting effects on their social variables. 4. O. c. cozumelae was distributed according to its age and sex: the proportion of adults and males was higher in interior than near edges, while juveniles and females were more abundant near edges. More nonreproductive females were present in corners than in single-edge and interior, while the opposite distribution was observed for nonreproductive males. 5. The distribution of R. spectabilis was related to its age and reproductive condition, but not to its sex. The proportion of adults was significantly higher in corners, while juveniles were only caught in single-edge and interior quadrants. The proportion of reproductive individuals was higher in edge than interior quadrants, while reproductive females were only present in edge quadrants. 6. We found significant differences between the quadrants with the greatest edge exposure in comparison with other quadrants. The social edge effects we identified complement the typology of edge effects recognized in ecological literature. Our study provides insight into the effects that sharp road edges have on biological and social characteristics of small mammal populations, highlighting how such effects vary among species. Our findings have important conservation implications for these threatened species, but are also applicable in a broader context wherever there are abrupt edges caused by linear landscape features.

Morphology of skin incubation in Pipa carvalhoi (Anura: Pipidae)

South American Pipidae show a unique reproductive mode, in which the fertilized eggs develop in temporarily formed brood chambers of the dorsal skin after eggs have been deposited on the back of the female. We studied the skin incubation of Pipa carvalhoi using light microscopy and scanning electron microscopy. The skin consists of a stratified epithelium with a one-layered stratum corneum, and the dermis. The dermis of the dorsal skin of nonreproductive and reproductive females lacks a distinct stratum compactum, which is typical for most anuran skins. The entire dermis shows irregularly arranged collagen bundles like a stratum spongiosum. Before egg laying, the skin swells, primarily by thickening and further by loosening of the middle zone of the dermis. In the epidermis, large furrows develop that are the prospective sites of egg nidation. The epidermis, which forms a brood chamber around the developing egg becomes bi-layered and very thin and lacks a stratum corneum. Further, the dermis loosens and becomes heavily vascularized. Egg carrying females do not have mature oocytes in their ovaries indicating a slow down or interruption of egg maturation during this period. Similarities with the brood pouch of marsupial frogs are discussed.

Seasonal patterns of winter flounder Pseudopleuronectes americanus abundance and reproductive condition on the New York Bight continental shelf

To resolve varied and sometimes conflicting accounts of spawning and habitat characteristics for winter flounder Pseudopleuronectes americanus, seasonal patterns in abundance and reproductive condition were investigated in the New York Bight, near the southern edge of their current reproductive range. Fish were collected from trawl surveys on the inner continental shelf from October 2006 to October 2007. Pseudopleuronectes americanus were most abundant during January and April surveys, were rarely collected in August, with intermediate abundances in June and October. Measurements of fish condition [hepato-somatic index (I(H)), condition factor (K) and the per cent dry mass of muscle tissue (%M(D))] and reproductive condition [gonado-somatic index (I(G))] were determined to evaluate seasonal changes in energy accumulation and depletion and reproduction. Males and females had similar patterns in body and reproductive condition, although the magnitude of change was greater for females. I(H) values were highest during spring and early summer, suggesting increased feeding following spawning. K and %M(D) increased through spring and summer then declined in the autumn and winter concurrent with gonadal development. Gonads began developing in the autumn, and in January, I(G) values approached spawning levels, with many spent individuals collected in spring. Within these general patterns, however, there was a large degree of variability among individuals, and a few mature non-reproductive ('skipped spawning') females were observed. In the period after spawning, increased energy intake, indicated by increased I(H), may influence reproductive output since this energy is gradually transferred to the muscle and used for gonadal development in the forthcoming year. The occurrence of ripening individuals on the inner continental shelf in January suggests that these fish either rapidly move into estuaries to spawn by February-March or they remain on the inner shelf to spawn, or some combination of these. Future studies should evaluate these possibilities, as both estuarine and inner shelf habitats are potentially affected by activities such as dredging, sand dredging and wind energy development.

Seasonal variation in hormonal responses of timber rattlesnakes (Crotalus horridus) to reproductive and environmental stressors

Data addressing adrenocortical modulation across taxonomic groups are limited, especially with regard to how female reproductive condition influences the sensitivity of the hypothalamus-pituitary-adrenal axis. We investigated seasonal and reproductive variation in basal and stress-induced hormone profiles in a population of free-ranging timber rattlesnakes (Crotalus horridus) in north-central Pennsylvania during spring (i.e., May), summer (i.e., July), and early fall (i.e., September). Baseline corticosterone concentrations varied seasonally and were significantly lower during the summer sampling period in July. We observed a significant negative relationship between baseline corticosterone and testosterone in male snakes, while baseline corticosterone and estradiol tended to be positively correlated in females. Treatment of snakes with 1 h of capture stress significantly increased corticosterone across all seasons. However, there was a significant interaction between corticosterone responses to capture stress and season, suggesting that adrenocortical function is modulated seasonally. Because elevated corticosterone may be associated with reproduction, we asked whether hormonal stress responses vary with female reproductive condition. Although sample sizes are low, reproductive snakes had significantly higher baseline and stress-induced corticosterone concentrations than non-reproductive or post-parturient females. Further, despite similar baseline corticosterone concentrations between non-reproductive and post-parturient rattlesnakes, post-parturient females responded to capture stress with a significantly higher increase in corticosterone. Collectively, these data suggest that the sensitivity of the hypothalamus-pituitary-adrenal axis varies both seasonally and with changing reproductive states.

Morphological Caste Differences in Polybia aequatorialis (Hymenoptera: Vespidae: Polistinae: Epiponini), a Social Wasp of the Highlands of Costa Rica

Many aspects of the biology and organization of Neotropical social wasps in the highlands are unknown. Polybia aequatorialis is a highland wasp of Costa Rica distributed between 1,150 and 3,200 m in altitude, and little information on this species is recorded. We investigated the size of a colony of P. aequatorialis in the Cerro de la Muerte region of Costa Rica, and studied the morphological differences between queens and workers. Measures were taken from 248 reproductive and non-reproductive females, and caste differentiation was analyzed by Discrimination Function Analysis. We did not find a highly pronounced caste distinction in P. aequatorialis, even though ANOVA showed that queens and workers differed in all morphometric measures. The morphological differences between the reproductive and non-reproductive females probably results from a developmental switch, which is a characteristic caste syndrome of Polybia.

Adaptive hearing in the vocal plainfin midshipman fish: getting in tune for the breeding season and implications for acoustic communication

The plainfin midshipman fish (Porichthys notatus Girard, 1854) is a vocal species of batrachoidid fish that generates acoustic signals for intraspecific communication during social and reproductive activity and has become a good model for investigating the neural and endocrine mechanisms of vocal-acoustic communication. Reproductively active female plainfin midshipman fish use their auditory sense to detect and locate "singing" males, which produce a multiharmonic advertisement call to attract females for spawning. The seasonal onset of male advertisement calling in the midshipman fish coincides with an increase in the range of frequency sensitivity of the female's inner ear saccule, the main organ of hearing, thus leading to enhanced encoding of the dominant frequency components of male advertisement calls. Non-reproductive females treated with either testosterone or 17β-estradiol exhibit a dramatic increase in the inner ear's frequency sensitivity that mimics the reproductive female's auditory phenotype and leads to an increased detection of the male's advertisement call. This novel form of auditory plasticity provides an adaptable mechanism that enhances coupling between sender and receiver in vocal communication. This review focuses on recent evidence for seasonal reproductive-state and steroid-dependent plasticity of auditory frequency sensitivity in the peripheral auditory system of the midshipman fish. The potential steroid-dependent mechanism(s) that lead to this novel form of auditory and behavioral plasticity are also discussed.

Reproductive Activity, Diet, and Microhabitat Use in Bolitoglossa nicefori (Caudata: Plethodontidae)

Bolitoglossa nicefori is a terrestrial salamander only known from its original description. We report the discovery of two populations of this species; analyze annual reproductive activity, diet, and microhabitat use of one population; and compare this information with that known for other species of Bolitoglossa. Sexually mature males ranged between 29 and 50 mm standard length and females between 39 and 75 mm. Histological analyses of testes and ducts revealed the presence of sperm through the year, indicating continuous reproductive activity for males. Adult females were captured year-round; however, reproductive females were observed only during the driest months of the year (November to February), indicating that females have a seasonal reproductive activity. The contents of 89 stomachs were analyzed, and perch height, type of vegetation, and substrate type were registered. The diet of this population consists of 13 items, with ants and coleopterans accounting for 87% of food ingested by the different age and sex classes. Ants represent 58% of the diet, reflecting their greater availability in this microhabitat. Intra- and intersexual differences in diet were not found. Bolitoglossa nicefori exhibited both terrestrial and arboreal behaviors related to temperature and humidity conditions during the daily cycle. Mature nonreproductive females, males, and juveniles were found perching from 0–60 cm above the ground on Araceae bushes that predominate in the study area, whereas reproductive females were always found within the leaf litter. Life-history features of B. nicefori are determined by environmental conditions; however, they follow common trends shared with other species of Bolitoglossa.

Steroid-dependent auditory plasticity for the enhancement of acoustic communication: Recent insights from a vocal teleost fish

The vocal plainfin midshipman fish ( Porichthys notatus) has become an excellent model for identifying neural mechanisms of auditory perception that may be shared by all vertebrates. Recent neuroethological studies of the midshipman fish have yielded strong evidence for the steroid-dependent modulation of hearing sensitivity that leads to enhanced coupling of sender and receiver in this vocal-acoustic communication system. Previous work shows that non-reproductive females treated with either testosterone or 17β-estradiol exhibit an increase in the degree of temporal encoding by the auditory saccular afferents to the dominant frequency content of male vocalizations produced during social-reproductive behaviors. The expanded frequency sensitivity of steroid treated females mimics the reproductive female’s auditory phenotype and is proposed to improve the detection and localization of calling conspecific mates during the summer breeding season. This review focuses on the novel form of steroid-dependent auditory plasticity that is found in the adult midshipman fish and its association with the reproductive biology and behavior of this species. Evidence for midshipman reproductive-state and steroid-dependent auditory plasticity is reviewed and the potential mechanisms that lead to this novel form of adaptive plasticity are discussed.

Broadening the focus of bat conservation and research in the USA for the 21st century

Appropriately, bat conservation in the USA during the 20th century focused on species that tend to aggregate in large numbers and locations (e.g. maternity roosts, hibernacula) where pop- ulations are most vulnerable. Extensive research into habitat needs (primarily for roosting) of repro- ductive females during the previous 2 decades has produced a wealth of information useful for devel- oping conservation strategies for this group in their summer roost areas. However, the ecological needs of males, non-reproductive females, and juveniles have received far less attention, as have the ecological needs of all bats outside the pup-rearing season. Hence, it is unlikely that a single para- digm could comprehensively address conservation needs of all demographic groups within a species because they may have different seasonal distributions, reproductive strategies, and thermoregula- tory needs. Herein, we recommend research into a wider spectrum of demographic groups and sea- sons to form a more holistic vision of the conservation needs of bats. We urge greater attention to understanding thermo-energetic and reproductive underpinnings of observed patterns of seasonal distribution and habitat selection by bats in the USA. Such understanding is instrumental for devel- opment of scientifically sound conservation strategies to confront emerging threats to conservation of bats in the 21st century: climate change, disease, habitat degradation, and environmental contami- nants. We discuss interconnections among these emerging threats and the fundamental need to incorporate understanding of thermo-energetic strategies of bats in development of conservation strategies or legislation to mitigate potential impacts on bat populations of the USA.

Agonistic Interactions Differ by Sex and Season in the Crayfish Orconectes Quinebaugensis

In many taxa, social structures are mediated by agonistic interactions and the formation of dominance hierarchies. In crayfish, dominance hierarchies may have evolved as a result of sexual selection, allowing dominant males greater access to females. We examine strategies of investment in agonistic behaviors for males and females of the crayfish Orconectes quinebaugensis in both the reproductive and non-reproductive seasons. We hypothesized that reproductive males would invest more in agonistic behaviors than reproductive females and non-reproductive crayfish. We tested this hypothesis in the laboratory with 4 treatment groups: males and females in the autumn reproductive season and males and females in the summer non-reproductive season, with each group subdivided by size to control for size effects. As predicted, reproductive males spent significantly more time in agonistic behaviors and had significantly more fights reaching maximum intensity than reproductive females, while there was no significant difference in the time spent in agonistic interactions by non-reproductive males or females. We did find that small females in the summer had significantly fewer fights reaching maximum intensity than either males or large females in the summer. However, there was no significant difference in time spent in agonistic interactions or proportion of fights reaching maximum intensity between reproductive males and non-reproductive males, as was predicted by our hypothesis. We did observe a significant effect of size for both males and females in the non-reproductive season, with larger animals spending more time in agonistic behaviors, and with large females having a more fights at maximum intensity than small females; this difference was not recapitulated in the reproductive season. These data indicate that investment in agonism differs by sex and by reproductive status, and the differential investment by sex in reproductive animals may indicate that dominance interactions are under sexual selection in males. However, high investment in agonism by both males and females in the non-reproductive season is not consistent with our hypothesis. Alternatively, the differential investment in agonism by reproductive males and females could be explained by either seasonal changes in the individual costs and benefits of agonism, or by depressed investment by reproductive females.

Allocating Protein to Reproduction in Arctic Reindeer and Caribou

Reindeer (Rangifer tarandus tarandus) and caribou (Rangifer tarandus granti) use body stores (capital) and food intake (income) for survival and reproduction. Intakes of low-nitrogen (N) food declined in winter and increased in spring (51-83 g dry matter kg(-0.75) d(-1)). Reindeer calved before regaining food intake, whereas caribou calved 28 d later. Body N was conserved by minimizing oxidation of amino acid N to urea. Maternal protein stored from early winter was used for 96% of fetal growth in reindeer but only 84% of fetal growth in later-birthing caribou. Both subspecies rely on maternal body protein for 91% of the protein deposited in the neonate via milk over the first 4 wk. All females lost body protein over winter, but lactating females continued to lose protein while nonreproductive females regained protein. Net costs of lactation above maintenance were greater for N (110%-130%) than for energy (40%-59%). Large fat stores in reindeer spare body protein from oxidation in winter, whereas in caribou, less fat with the same body protein favors migration when food is inadequate. The resilience of Rangifer populations to variable patterns of food supply and metabolic demand may be related to their ability to alter the timing and allocation of body protein to reproduction.