Jorge A. Encarnação

Reproductive condition and activity pattern of male Daubenton's bats (Myotis daubentonii) in the summer habitat

Summary We studied temporal variation in epididymal filling (a measure of reproductive condition) and activity pattern of male Daubentons bats (Myotis daubentonii) in a summer habitat near Staufenberg (Hesse, Germany). Epididymal filling in adult males declined from April to early July. Thereafter epididymal filling sharply increased and the highest median value was reached in the second half of September, i. e., prior to the occupation of the hibernaculum. Highest median epididymal filling in juveniles occurred in the first half of September. During August, September and October epididymal filling of adult males was significantly higher than that of juveniles. In late summer (August/September) relatively heavy adult males stayed significantly longer in their day roosts and spent significantly less time foraging than in early summer (June/July). The findings suggest that a large proportion of matings in M.daubentonii occurs already in the day roosts within the summer habitat.

Small scale distribution patterns of female and male Daubenton's bats (Myotis daubentonii)

ABSTRACT We analysed the distribution and relative abundance of Myotis daubentonii in the lowlands and uplands around the Lahn river near the city of Giessen (Hessen, Central Germany). We assumed a positive correlation between distribution and relative abundance of the trawling M. daubentonii with the amount of water surface in our study area. We further expected an unequal distribution of male and female M. daubentonii especially during the energy demanding pregnancy and lactation period of females. Daubentons bats were found at 75% of the 64 ponds and lakes we surveyed by standardized nightly spotlight counts. The number of Daubentons bats correlated positively with the area of the water surface and negatively with the distance to the nursery colonies. Nursery colonies were located with radio-tracking and existed predominantly in the lowlands close to the Lahn river. Mean flight distance between nursery colonies and foraging areas was 2.3 km (mean ± 1.4 km, range: 0.6–6.3 km). Sex ratio was determined at three sites studied in detail from 1992–2003 by mist-netting along regular used flight paths (n = 1,847 caught individuals). The number of female per male M. daubentonii was unequal and differed significantly between the three sites. In the lowland we found one site clearly dominated by females (median = 4.3 females per male, percentages of females 79.3%, n = 169 individuals) and a second site with an almost balanced sex ratio (median = 1.1 females per male, percentages of females 50.3%, n = 939 individuals). At the third site in the uplands males outnumbered females (median = 0.2 females per male, percentages of females 13.5%, n = 739 individuals). The percentages of females remained largely constant from spring to mid summer and changed at the beginning of September. The study revealed that a detailed knowledge of the spatial distribution of gender specific roost sites and key foraging habitats is necessary for the establishment of meaningful monitoring and conservation measures for bats.

Insectivorous Bats Digest Chitin in the Stomach Using Acidic Mammalian Chitinase

The gastrointestinal tract of animals is adapted to their primary source of food to optimize resource use and energy intake. Temperate bat species mainly feed on arthropods. These contain the energy-rich carbohydrate chitin, which is indigestible for the endogenous enzymes of a typical mammalian gastrointestinal tract. However, the gastrointestinal tract of bat species should be adapted to their diet and be able to digest chitin. We hypothesized that (i) European vespertilionid bat species have the digestive enzyme chitinase and that (ii) the chitinolytic activity is located in the intestine, as has been found for North American bat species. The gastrointestinal tracts of seven bat species (Pipistrellus pipistrellus, Plecotus auritus, Myotis bechsteinii, Myotis nattereri, Myotis daubentonii, Myotis myotis, and Nyctalus leisleri) were tested for chitinolytic activity by diffusion assay. Gastrointestinal tracts of P. pipistrellus, P. auritus, M. nattereri, M. myotis, and N. leisleri were examined for acidic mammalian chitinase by western blot analysis. Tissue sections of the gastrointestinal tract of P. pipistrellus were immunohistochemically analyzed to locate the acidic mammalian chitinase. Chitinolytic activity was detected in the stomachs of all bat species. Western blot analysis confirmed the acidic mammalian chitinase in stomach samples. Immunohistochemistry of the P. pipistrellus gastrointestinal tract indicated that acidic mammalian chitinase is located in the stomach chief cells at the base of the gastric glands. In conclusion, European vespertilionid bat species have acidic mammalian chitinase that is produced in the gastric glands of the stomach. Therefore, the gastrointestinal tracts of insectivorous bat species evolved an enzymatic adaptation to their diet.

Body mass changes in male Daubenton's bats Myotis daubentonii (Chiroptera, Vespertilionidae) during the seasonal activity period

Body mass changes of adult and juvenile male Daubenton’s bats were studied in a summer habitat in Hesse (Germany) in the years 1998-2001. Animals from the resident population were regularly captured along the flight path from April to October, and body mass was determined using a digital balance. Body mass of adult individuals differed significantly among fortnightly periods (Kruskal-Wallis ANOVA by ranks: H = 141.75, p < 0.001). Body mass increased significantly from the second half of April (median: 7.0 g) to the first half of May (median: 7.8 g). Between the second half of May and the first half of August, median body mass fluctuated between 7.8 g and 8.3 g. From the second half of July (median: 7.9 g) to the second half of August (median: 8.4 g), and the second half of September (median: 9.3 g) body mass again significantly increased. The highest median body mass (9.6 g) was recorded in the second half of October. Median body mass of juvenile males ranged between 6.5 g in the first half of July and 8.5 g in the second half of October. Differences in body mass over the studied period were significant (H = 21.70, p < 0.01). During the months July, August, and September, body mass of adult males was significantly higher than that of juveniles, whereas in October the difference was no longer of statistical significance. It is suggested that the decrease in body mass observed in some adult males in September was related to their reproductive activity.

Balancing the Energy Budget in Free-Ranging Male Myotis daubentonii Bats

Mammals use five main, mutually nonexclusive mechanisms to balance energy budgets: torpor, metabolic compensation, change in activity patterns, change in ingested energy, and/or variability in digestive efficiency. Bats, as small and actively flying mammals, have a high mass-specific energy demand; therefore, balancing mechanisms should be pronounced in this group. We found that male Myotis daubentonii exhibited marked variation in the relative importance of these different mechanisms during their period of seasonal activity in response to extrinsic (ambient temperature, insect abundance) and intrinsic (reproduction, body condition) factors. Cold ambient temperatures in spring facilitated long and frequent daily torpor bouts, whereas in early summer, increased energy intake was the dominant factor in energy balancing. Intake was further increased in late summer, when insect abundance was highest, and daily torpor bouts were shorter and less frequent than in early summer. In autumn, males used metabolic compensation to reduce their resting metabolic rate in addition to daily torpor. Metabolic compensation might be one of the mechanisms that allow males to maintain high body temperature during the day while decreasing the need for foraging time at night, thus maximizing their opportunities to mate.

Energetics and life-history of bats in comparison to small mammals

Mammals can be aligned along a slow-fast life-history continuum and a low–high metabolic rate continuum based on their traits. Small non-volant mammals occupy the fast/high end in both continua with high reproductive rates and short life spans linked with high mass-specific metabolic rates. Bats occupy the high end of the metabolic continuum, but the slow end of the life-history continuum with low reproductive rates and long life spans. Typically, both continua are linked, and similar life-history traits of species are reflected in more similar metabolic rates. We therefore hypothesized that metabolic rates are similar in species with similar life-history traits. Resting metabolic rates (RMR) were measured for three ecologically and morphologically similar sympatric bat species (Myotis nattereri, M. bechsteinii, and Plecotus auritus; Vespertilionidae) and compared to data from other similar-sized, temperate insectivorous mammals with other life-history strategies. The bat species share similar life-histories and RMRs, both of which differ from the remaining mammals and therefore supporting our hypothesis. To verify that bats are similar in RMR, two energetically contrasting periods were compared. RMRs in post-lactating females did not differ between bat species. It was, however, positively correlated with parasite load in both Myotis species. However, RMRs differed during energy-demanding pregnancy where M. nattereri had the significantly lowest RMR, suggesting metabolic compensation as an energy-saving strategy. We conclude that the energy requirements of bat species with similar life-history traits resemble each other during periods of low energetic demands and are more similar to each other than to other small temperate mammals.

Seasonal Variations of Wing Mite Infestations in Male Daubenton'S Bats (Myotis daubentonii) in Comparison to Female and Juvenile Bats

In this study, the physiological and behavioural factors that influence infestation levels of wing mites on a large sample of Daubentons bat (Myotis daubentonii) were investigated. This is the first study to present a comprehensive data set that includes male M. daubentonii over the entire seasonal activity period. In males, parasite load increased during spermatogenesis, which can be explained by high testosterone levels acting as an immunosuppressant. Prevalence rates and infestation levels in males were always lower than those of females and juveniles, possibly due to grooming behaviour which may be energetically restricted in females and inefficient in juveniles. Colony size did not appear to influence parasite load in males, but was found to have an influence in females and juveniles. Larger group sizes in males might not increase parasite load since grooming behaviour and roost switching are frequent. This study showed that parasite load in free-ranging Daubentons bats is sex-, season- and age-specific due to variations in behaviour and physiology.

AGE-RELATED VARIATION IN PHYSICAL AND REPRODUCTIVE CONDITION OF MALE DAUBENTON'S BATS (MYOTIS DAUBENTONII)

Abstract We studied age-related variation in body mass and epididymal distension in male Daubentons bats. Examination of data on epididymal distension in young of the year indicates that some reach sexual maturity by the year of birth, whereas others do so in their 2nd summer. Body mass and epididymal distension were positively correlated in young of the year and adults, suggesting that early sexual maturation and reproductive condition during later life are dependent on body condition. Older males tended to be heavier and in better reproductive condition than younger ones. Examination of our data suggests that physical and reproductive condition of males increase after the initial onset of fertility until 3 years of age. This late physical maturation is in line with other life-history traits characterizing long-lived bats as K-strategists among small mammals.

The effects of reproductive state on digestive efficiency in three sympatric bat species of the same guild

The functional link between food as an energy source and metabolizable energy is the digestive tract. The digestive organs may change in size, structure, or retention time in response to energetic demands of the animal. Very efficient digestive tracts may be better at processing food but require higher energetic investments for maintenance even when post-absorptive. These costs influence the resting metabolic rate (RMR) that is defined as the energy necessary to fuel vital metabolic functions in a resting animal. In bats a trade-off between the necessity for a highly efficient digestive tract and moderate energetic maintenance costs may be particularly important. We hypothesized that low RMR coincides with low digestive efficiency (defined as apparent metabolizable energy coefficient (MEC)) and that phases of increased energetic demand are compensated for by increased digestive efficiency. We measured RMR and apparent MEC in the bats species Myotis nattereri, M. bechsteinii, and Plecotus auritus. In support of our hypothesis, M. nattereri has the lowest mass-specific RMR of the three species and the lowest apparent MEC. However, apparent MEC did not change during phases with differing energetic demands in any of the bat species, probably because bats operate at the limit of their sustainable energy demand.

An optimized hair trap for non-invasive genetic studies of small cryptic mammals

As sample quality and quantity is a crucial factor in non-invasive genetics, we focused on the improvement of sampling efficiency of glue hair traps. We invented an optimized hair trap with moveable parts which enhanced sampling of high-quality genetic material. With the aid of the optimized hair trap, we were able to remotely pluck a sufficient amount of hair bulbs from our study animal the common hamster (Cricetus cricetus) with a trapping success of 49.3% after one survey night. The number of collected hairs with bulbs ranged between 1 and 50, with an average of 20.7 ± 14.8. Subsequently, the use of the hair trap in combination with a simplified laboratory routine allowed us to amplify species-specific microsatellites with an amplification success of 96.2% and ADO of 4.6%. This optimized trap may find usage for species identification or could be used as an instrument for long-term genetic monitoring of mammal populations.