Carina Siutz

Sex and age differences in hibernation patterns of common hamsters: adult females hibernate for shorter periods than males

In this study, we investigated the timing and duration of hibernation as well as body temperature patterns in free-ranging common hamsters (Cricetus cricetus) with regard to sex and age differences. Body temperature was recorded using subcutaneously implanted data loggers. The results demonstrate that although immergence and vernal emergence sequences of sex and age groups resembled those of most hibernators, particularly adult females delayed hibernation onset until up to early January. Thus, in contrast to other hibernators, female common hamsters hibernated for shorter periods than males and correspondingly spent less time in torpor. These sex differences were absent in juvenile hamsters. The period between the termination of hibernation and vernal emergence varied among individuals but did not differ between the sex and age groups. This period of preemergence euthermy was related to emergence body mass: individuals that terminated hibernation earlier in spring and had longer euthermic phases prior to emergence started the active season in a better condition. In addition, males with longer periods of preemergence euthermy had larger testes at emergence. In conclusion, females have to rely on sufficient food stores but may adjust the use of torpor in relation to the available external energy reserves, whereas males show a more pronounced energy-saving strategy by hibernating for longer periods. Nonetheless, food caches seem to be important for both males and females as indicated by the euthermic preemergence phase and the fact that some individuals, mainly yearlings, emerged with a higher body mass than shortly before immergence in autumn.

Sex Differences in Foraging Behaviour, Body Fat and Hibernation Patterns of Free-Ranging Common Hamsters

In this study, we investigated foraging behaviour, body fat and hibernation patterns in adult common hamsters (Cricetus cricetus). In addition, we compared the proportion of body fat prior to hibernation between adult and juvenile individuals. We investigated a population of free-ranging common hamsters in an urban area in southern Vienna, Austria. We applied capture-mark-recapture techniques and focal-animal-sampling for behavioural recordings. Body fat was calculated by integrating morphometric parameters. Body temperature changes were recorded during winter using subcutaneously implanted data loggers. We calculated the time individuals spent in torpor, the number and length of torpor bouts. The results revealed sex differences in foraging behaviour, in that males were feeding mainly above ground, whereas females almost exclusively cached food. These potential differences in energy allocation prior to winter were reflected in body fat at the end of the active season. Adult males had a higher proportion of body fat than females. Although juveniles had lower body fat than adults, similar sex differences were found. During winter adult males spent more time in torpor than females, indicating differing overwintering strategies depending on the individual potential to allocate internal or external energy reserves.

The common hamster as a synurbist: a history of settlement in european cities

Abstract Following the expansion of agriculture in the Neolithic period, the common hamster has spread throughout Europe, and occurred abundantly until the recent past. However, in the last 45 years, populations declined markedly, partly attributable to urbanization and to major changes in agricultural practices. As a result, the species has been considered endangered at international levels as well as in most European countries. At the same time, the species has established populations in large Central and Eastern-European cities such as Vienna (Austria), Simferopol (Ukraine) and Nalchik (Russia), where it inhabits green spaces such as parks, gardens, embankments and buffer strips. In an attempt to reveal factors enabling hamsters to cope with urban environments, we reviewed historical data and habitat conditions of several urban hamster populations. We suggest that supplemental food resources and reduced predation pressure were the main factors promoting urban occurrence of common hamsters in the last 30 years. Its notable adaptability may be associated with higher stress resilience, ecological opportunism, polyphagy and higher fertility compared to species relying on non-urban habitats. The phenomenon of synurbization implies coexistence of wildlife and our urban civilization, but at the same time conflicting interests in conservation and urban development. Thus, the common hamster might serve as a model species for efficient mitigation and compensation concepts in urbanism and spatial planning. STRESZCZENIE Chomik europejski rozprzestrzenił się w Europie w następstwie rozwoju rolnictwa w Neolicie i do niedawna występował bardzo licznie. Jednak w ciągu ostatnich 45 lat. liczebność populacji wyraźnie spadła częściowo ze względu na urba- nizację i znaczące zmiany w rolnictwie. W efekcie gatunek jest obecnie uważany za zagrożony zarówno na poziomic międzynarodowym, jak i w poszczególnych państwach europejskich. Jednocześnie jednak powstały populacje w dużych miastach Europy Centralnej i Wschodniej, na przykład w Wiedniu (Austria), Symferopolu (Ukraina) i Nalchiku (Rosja), gdzie chomik zamieszkuje tereny zielone takie jak parki, ogrody na nabrzeżach rzek i pasy buforowe. W celu ustalenia czyn- ników umożliwiających chomikom dostosowanie do warunków zurbanizowanych, stworzyliśmy przegląd danych historycznych i warunków siedliskowych w kilku miejskich populacjach chomika. Sugerujemy, że dodatkowe źródła pokarmu i zmniejszony nacisk drapieżników były głównymi czynnikami sprzyjającymi występowaniu chomika europejskiego w miastach w ciągu ostatnich 30 lat. Szczególna adaptacyjność chomika może być związana z wyższą odpornością na stres, ekologicznym oportunizmem, wszystkożcmością i wyższą płodnością w porównaniu do gatunków polegających na niczurbanizowanych siedliskach. Fenomen synurbizacji zakłada współistnienie przyrody i naszej miejskiej cywilizacji, ale w tym samym czasie przeciwstawne interesy ochrony i rozwoju urbanistycznego. Tak więc chomik europejski może posłużyć za gatunek modelowy dla idei skutecznego łagodzenia konfliktów i wyrównywania strat w urbanistyce i plano- waniu przestrzennym.

Effects of birth date and natal dispersal on faecal glucocorticoid concentrations in juvenile Common hamsters.

Highlights ► Birth date and timing of dispersal affected cortisol secretion in juvenile Common hamsters. ► Late-born juveniles had elevated faecal cortisol metabolite (FCM) concentrations shortly after weaning. ► Juveniles that immigrated late in the season had higher FCM levels than early immigrants and residents. ► Elevated FCM levels in late immigrants were independent of birth date. ► Late-borns and late immigrants had less time to prepare for hibernation.

Torpor patterns in common hamsters with and without access to food stores

Hibernating species significantly reduce energy expenditure during winter by entering torpor. Nevertheless, the various benefits of hibernation might be counteracted by negative effects of torpor such as immune depression, oxidative stress, or neuronal impairment. Considering these trade-offs, adequate energy reserves could allow animals to reduce the time spent in torpor or the extent of metabolic depression. Common hamsters use food stores during hibernation and previously documented high individual variations in body temperature patterns during winter could, therefore, be related to differences in external energy reserves. In this study, we manipulated the availability of food stores under laboratory conditions to investigate potential effects on hibernation patterns. Female hamsters were kept in artificial burrows in climate chambers and subcutaneous temperature was recorded using implanted data loggers. One group had access to large food stores, whereas another group received daily food portions which were removed on the next day if not consumed. Almost all hamsters without access to food stores hibernated, while less than half of the individuals with food stores entered deep torpor. Individuals without food hoards additionally expressed more short torpor bouts and exhibited lower minimum subcutaneous temperatures during torpor than those with food stores. Thus, individuals confronted with lacking food reserves were more likely to hibernate and additionally saved energy by entering short torpor bouts more frequently and remaining at lower subcutaneous temperature both during torpor and euthermic periods. In conclusion, our results demonstrate that food store availability affects torpor expression and also highlight variation in torpor patterns and energy-saving strategies in common hamsters.

Stable isotope analysis as a minimal-invasive method for dietary studies on the highly endangered Common hamster (Cricetus cricetus)

Abstract This study applied the analysis of stable isotope ratios as a minimally-invasive tool to estimate the diet of Cricetus cricetus for the first time. We took hair and food samples of three different populations of C. cricetus and analyzed stable carbon and nitrogen ratios. The stable isotope ratios in hamster hairs differed significantly within and between populations according to different sampling seasons and animal ages. Additionally, the isotopic signatures of potential food samples differed between sampling sites and food categories. The isotopic mixing models illustrated that diet composition varied with season and food availability. During the summer season hamsters living in agricultural areas mainly fed on green and ripe crop. In contrast to this, during the winter season ripe crop was the main food component for hamsters in agricultural areas while hamsters living in urban areas fed almost exclusively on nuts. These are, despite a wide variety of available food sources, most suitable for hoarding in the burrow. We conclude that stable isotope analysis of hamster hairs is an appropriate minimal-invasive method to investigate correlations between available and consumed food sources throughout the overall distribution of this species.

Effects of food store quality on hibernation performance in common hamsters

Hibernating animals can adjust torpor expression according to available energy reserves. Besides the quantity, the quality of energy reserves could play an important role for overwintering strategies. Common hamsters are food-storing hibernators and show high individual variation in hibernation performance, which might be related to the quality of food hoards in the hibernacula. In this study, we tested the effects of food stores high in fat content, particularly polyunsaturated fatty acids (PUFAs), on hibernation patterns under laboratory conditions. Control animals received standard rodent pellets only, while in the other group pellets were supplemented with sunflower seeds. We recorded body temperature during winter using subcutaneously implanted data loggers, documented total food consumption during winter, and analysed PUFA proportions in white adipose tissue (WAT) before and after the winter period. About half of the individuals in both groups hibernated and torpor expression did not differ between these animals. Among the high-fat group, however, individuals with high sunflower seeds intake strongly reduced the time spent in deep torpor. PUFA proportions in WAT decreased during winter in both groups and this decline was positively related to the time an individual spent in deep torpor. Sunflower seeds intake dampened the PUFA decline resulting in higher PUFA levels in animals of the high-fat group after winter. In conclusion, our results showed that common hamsters adjusted torpor expression and food intake in relation to the total energy of food reserves, underlining the importance of food hoard quality on hibernation performance.

Developmental patterns and body fat content of juvenile common hamsters (Cricetus cricetus l.)

Abstract The common hamster (Cricetus cricetus) is a facultative hibernator producing up to three litters per year. Juveniles born late in the season have less time to grow and prepare for the winter than early-born ones. We investigated a free-ranging population in an urban environment in Vienna, Austria. We compared body mass, proportion of body fat, as well as head, tibia and hind foot length between juveniles of first and second litters at natal emergence, four weeks post-emergence and shortly before onset of hibernation. In addition we tested for differences in growth rates during the first four weeks after emergence and for potential effects of sex and litter size. Capture-mark-recapture techniques were applied. Body fat content was calculated using a multiple regression model integrating morphometric parameters. At natal emergence, second litter offspring were larger and heavier than those of first litters. Litter size did not account for these differences. During the first week after natal emergence, first litter pups gained body mass faster, and during the first two weeks also showed faster head and tibia growth rates than second litter pups. Four weeks after natal emergence, however, second litter juveniles were still larger and heavier than first litter ones. Body fat content four weeks post-emergence did not differ between first and second litters but decreased with litter size. Shortly before onset of hibernation, however, first litter juveniles, which had more time to grow and accumulate body fat, exceeded second-litter ones in all measured parameters. In all litters investigated, we found no sex difference at natal emergence but males were heavier and larger than females four weeks thereafter demonstrating that the commonly known sexual dimorphism in this species developed during this period. Considering the time constraints late born juveniles face, the con ditional advance at natal emergence is assumed to be adaptive by increasing the chances for these individuals to survive overwinter despite the limited time to prepare for the hibernation period STRESZCZENIE Chomik europejski (Cricetus cricetus) jest gatunkiem hibernującym, który może mieć do trzech miotów rocznie. Osobniki urodzone pod koniec sezonu aktywności mają mniej czasu na wzrost i przygotowanie się do zimy niż młode urodzone na początku sezonu. Przeprowadziliśmy badania na wolno żyjącej, miejskiej populacji chomika we Wiedniu w Austrii. Porównaliśmy masę ciała, zawartość tkanki tłuszczowej, a także długość głowy, piszczeli oraz tylnej stopy pomiędzy osobnikami z pierwszego i drugiego miotu zaraz po pierwszym wyjściu z nory, cztery tygodnie po opuszczeniu nory oraz zaraz przed rozpoczęciem hibernacji. Dodatkowo porównaliśmy tempo wzrostu podczas czterech pierwszych tygodni od pierwszego opuszczenia nory oraz przeanalizowaliśmy dane w celu stwierdzenia obecności efektu płci i wielkości miotu. Dane pozyskaliśmy stosując metodę odłowów CMR. Zawartość tkanki tłuszczowej została obliczona na postawie modelu wielokrotnej regresji uwzględniając parametry morfometryczne. Po- tomstwo z drugiego miotu podczas pierwszego wyjścia z nory było większe i cięższe niż osobniki z pierwszego miotu. Różnica ta nic była powiązana z wielkością miotu. Podczas pierwszego tygodnia po wyjściu z nory osobniki z pierwszego miotu przybierały na masie szybciej, a także w pierwszych dwóch tygodniach wykazywały szybszy wzrost głowy i piszczeli. Jednakże cztery tygodnie po wyjściu z nory to młode z drugiego miotu były nadal większe i cięższe niż młode z pierwszego miotu. Badania zwartości tkanki tłuszczowej cztery tygodnie po wyjściu potomstwa z nory nie wykazały różnic pomiędzy pierwszym a drugim miotem, wykazały nato[niast zależność między wielkością miotu a spadkiem zawartości tłuszczu. Krótko przed rozpoczęciem hibernacji to młode z pierwszego miotu, które miały więcej czasu na wzrost i zgromadzenie tłuszczu, prze- wyższyły osobniki z drugiego miotu we wszystkich badanych parametrach. W żadnym z badanych miotów nic zaobserwowano różnic pomiędzy płciami w trakcie pierwszego wyjścia młodych z nory. Jednak cztery tygodnie później to samce były większe i cięż- sze, co pokazuje, że dymorfizm płciowy obserwowany powszechnie u tego gatunku kształtuje się właśnie w tym okresie. Biorąc pod uwagę ograniczenie czasowe, z którym muszą się zmierzyć młode urodzone późno, zakłada się, że ich większe rozmiary i masa ciała mają na celu zwiększenie szans przetrwania zimy, pomimo ograniczonego czasu na przygotowanie się do hibernacji.

Sex-specific effects of food supplementation on hibernation performance and reproductive timing in free-ranging common hamsters

Hibernation is characterized by reduced metabolism and body temperature during torpor bouts. Energy reserves available during winter play an important role for hibernation and some species respond to high energy reserves with reduced torpor expression. Common hamsters are food-storing hibernators and females hibernate for shorter periods than males, probably related to larger food stores. In this study, we provided free-ranging common hamsters with sunflower seeds shortly before winter and recorded body temperature using subcutaneously implanted data loggers. We compared hibernation patterns and body mass changes between individuals with and without food supplements and analysed reproductive onset in females. Supplemented males delayed hibernation onset, hibernated for much shorter periods, and emerged in spring with higher body mass than unsupplemented ones. Additional food did not affect hibernation performance in females, but supplemented females emerged earlier and preceded those without food supplements in reproductive onset. Thus, males and females differently responded to food supplementation: access to energy-rich food stores enabled males to shorten the hibernation period and emerge in better body condition, probably enhancing mating opportunities and reproductive success. Females did not alter hibernation patterns, but started to reproduce earlier than unsupplemented individuals, enabling reproductive benefits by an extended breeding period.

Steroid hormone concentrations and body mass are differently affected by polyunsaturated fatty acids during the oestrous cycle in guinea pigs

Reproductive functions in female mammals can be significantly affected by the actions of dietary polyunsaturated fatty acids (PUFAs) on steroid hormone secretion rates. Nevertheless, the effects of plasma free PUFAs on the oestrous cycle have seldom been considered. Therefore, in the present study, the diet of domestic guinea pigs was supplemented with high concentrations of different PUFAs and the effects of altered plasma PUFA patterns on steroid hormone concentrations, measured non-invasively, and body mass during oestrus and dioestrus were analysed. The oestrous cycle was characterised by increased oestrogen and cortisol concentrations in oestrus, corroborated by lowest bodyweight, whereas progesterone concentrations were highest in dioestrus. Plasma concentrations of the long-chain PUFAs docosahexaenoic acid (DHA; 22:6 ω3) and arachidonic acid (AA; 20:5 ω6) affected steroid hormone concentrations differently in oestrus and dioestrus. DHA positively affected oestrogen and progesterone concentrations and diminished cortisol concentrations only in oestrus. In contrast, AA negatively affected oestrogen and stimulated cortisol concentrations in oestrus and reduced progesterone concentrations in general. These findings imply selective and opposite contributions of DHA and AA to ovarian functions during different stages of the oestrous cycle, indicating a high biological relevance of plasma free PUFAs in female reproductive function.