Generational shift in the migratory common noctule bat: first-year males lead the way to hibernacula at higher latitudes.

Many migratory species have shifted their geographic distribution in response to climate change, yet the underlying mechanisms are poorly understood, particularly for mammals. We hypothesized that generational shifts are underlying the observed colonization of hibernation sites further north in a migratory bat, the common noctule (Nyctalus noctula). To evaluate our hypothesis, we collected long-term data on the migratory status and demography of common noctules in a recently colonized hibernation area. Based on isotopic data of 413 individuals, we observed a significant decline in the proportion of long-distance migrants from 2004 to 2015 for both sexes and across all age groups. Demographic data collected between 2007 and 2016 from 3394 individuals demonstrated that subadult males were more abundant during the early colonization stage, followed by a gradual shift to a more balanced age and sex composition. Our results suggest that the colonization of hibernacula at higher latitudes is promoted by generational shifts, involving mostly first-year males. Generational shifts seem to be a likely mechanism for distribution changes in other bats and potentially also in other mammals.

Individual variation of isotopic niches in grazing and browsing desert ungulates.

Ungulates often adjust their diet when food availability varies over time. However, it is poorly understood when and to what extent individuals change their diet and, if they do so, if all individuals of a population occupy distinct or similar dietary niches. In the arid Namibian Kunene Region, we studied temporal variations of individual niches in grazing gemsbok (Oryx gazella gazella) and predominantly browsing springbok (Antidorcas marsupialis). We used variation in stable C and N isotope ratios of tail hair increments as proxies to estimate individual isotopic dietary niches and their temporal plasticity. Isotopic dietary niches of populations of the two species were mutually exclusive, but similar in breadth. Isotopic niche breadth of gemsbok was better explained by within-individual variation than by between-individual variation of stable isotope ratios, indicating that gemsbok individuals were facultative specialists in using isotopically distinct local food resources. In contrast, inter- and intra-individual variations contributed similarly to the isotopic niche breadth of the springbok population, suggesting a higher degree of individual isotopic segregation in a more generalist ungulate. In both species, between-individual variation was neither explained by changes in plant primary productivity, sex, geographical position nor by group size. Within species, individual dietary niches overlapped partially, suggesting that both populations included individuals with distinct isotopic dietary niches. Our study provides the first evidence for isotopic dietary niche segregation in individuals of two distinct desert ungulates. Similar, yet isotopically distinct dietary niches of individuals may facilitate partitioning of food resources and thus individual survival in desert ecosystems.

Trophic flexibility and opportunism in pike Esox lucius.

The first comprehensive investigation of pike Esox lucius trophic ecology in a region (Ireland) where they have long been thought to be a non-native species is presented. Diet was investigated across habitat types (lake, river and canal) through the combined methods of stable-isotope and stomach content analyses. Variations in niche size, specialization and the timing of the ontogenetic dietary switch were examined, revealing pronounced opportunism and feeding plasticity in E. lucius, along with a high occurrence of invertivory (up to 60 cm fork length, LF ) and a concomitant delayed switch to piscivory. Furthermore, E. lucius were found to primarily prey upon the highly available non-native roach Rutilus rutilus, which may alleviate predation pressure on brown trout Salmo trutta, highlighting the complexity of dynamic systems and the essential role of research in informing effective management.

MHC class II DRB diversity, selection pattern and population structure in a neotropical bat species, Noctilio albiventris.

Genes of the major histocompatibility complex (MHC) have a crucial role in the immune response of vertebrates, alter the individual odour and are involved in shaping mating preferences. Pathogen-mediated selection, sexual selection and maternal-fetal interactions have been proposed as the main drivers of frequently observed high levels of polymorphism in functionally important parts of the MHC. Bats constitute the second largest mammalian order and have recently emerged as important vectors of infectious diseases. In addition, Chiroptera are interesting study subjects in evolutionary ecology in the context of olfactory communication, mate choice and associated fitness benefits. Thus, it is surprising that they belong to the least studied mammalian taxa in terms of their MHC diversity. In this study, we investigated the variability in the functionally important MHC class II gene DRB, evidence for selection and population structure in the group-living lesser bulldog bat, Noctilio albiventris, in Panama. We found a single expressed, polymorphic Noal-DRB gene. The substitution pattern of the nucleotide sequences of the 18 detected alleles provided evidence for positive selection acting above the evolutionary history of the species in shaping MHC diversity. Roosting colonies were not genetically differentiated but females showed lower levels of heterozygosity than males, which might be a sign that the sexes differ in the selection pressures acting on the MHC. This study provides the prerequisites for further investigations of the role of the individual MHC constitution in parasite resistance, olfactory communication and mate choice in N. albiventris and other bats.

Fruit bats (Pteropodidae) fuel their metabolism rapidly and directly with exogenous sugars.

Previous studies reported that fed bats and birds mostly use recently acquired exogenous nutrients as fuel for flight, rather than endogenous fuels, such as lipids or glycogen. However, this pattern of fuel use may be a simple size-related phenomenon because, to date, only small birds and bats have been studied with respect to the origin of metabolized fuel, and because small animals carry relatively small energy reserves, considering their high mass-specific metabolic rate. We hypothesized that approximately 150 g Egyptian fruit bats (Rousettus aegyptiacus Pteropodidae), which are more than an order of magnitude heavier than previously studied bats, also catabolize dietary sugars directly and exclusively to fuel both rest and flight metabolism. We based our expectation on the observation that these animals rapidly transport ingested dietary sugars, which are absorbed via passive paracellular pathways in the intestine, to organs of high energy demand. We used the stable carbon isotope ratio in exhaled CO(2) (delta(13)C(breath)) to assess the origin of metabolized substrates in 16 Egyptian fruit bats that were maintained on a diet of C3 plants before experiments. First, we predicted that in resting bats delta(13)C(breath) remains constant when bats ingest C3 sucrose, but increases and converges on the dietary isotopic signature when C4 sucrose and C4 glucose are ingested. Second, if flying fruit bats use exogenous nutrients exclusively to fuel flight, we predicted that delta(13)C(breath) of flying bats would converge on the isotopic signature of the C4 sucrose they were fed. Both resting and flying Egyptian fruit bats, indeed, directly fuelled their metabolism with freshly ingested exogenous substrates. The rate at which the fruit bats oxidized dietary sugars was as fast as in 10 g nectar-feeding bats and 5 g hummingbirds. Our results support the notion that flying bats, irrespective of their size, catabolize dietary sugars directly, and possibly exclusively, to fuel flight.

Pregnancy diagnosis in urine of Iberian lynx (Lynx pardinus).

Diagnosis of pregnancies is an important management tool for the Iberian lynx Conservation Breeding Program, a program geared to recover the world's most endangered felid. Non-invasive methods such as fecal hormone analyses are not applicable to the lynx, since fecal progestin does not follow the typical pregnancy pattern of felids. Therefore, we aimed to test whether urine can be used as an alternative substance for pregnancy diagnosis in the Iberian lynx. Progesterone immunoreactive metabolites were determined in urine samples of pregnant and non-pregnant females before and during breeding season. Additionally, we used the Witness Relaxin test to determine relaxin in blood and urine. No differences were found in progestin concentrations determined in urine samples collected from pregnant and non-pregnant animals between day 1 and 65 following mating. Although the Witness Relaxin test was positive in serum samples collected from animals between day 32 and 56 of pregnancy, it failed in both fresh and frozen urine samples collected from the same stage of pregnancy. A weak relaxin reaction in urine samples collected from animals between day 29 and 46 of pregnancy was detectable after urines were concentrated by ultrafiltration (>50x). Concentrated samples obtained from non-pregnant and early pregnant animals yielded negative test results. In conclusion, the Witness Relaxin test can be applied for pregnancy diagnosis in Iberian lynx in both serum and concentrated urine samples obtained during the second half of pregnancy. A positive relaxin test indicates an ongoing pregnancy, whereas negative tests must be judged carefully as hormone concentrations might be below detection thresholds.

Reproductive energetics of the nectar-feeding bat Glossophaga soricina (Phyllostomidae).

Pregnancy and lactation are energetically demanding periods for female mammals. Unique amongst mammals, bats have to allocate considerable amounts of energy into their offspring because juveniles cannot be weaned until they are capable of flying at almost adult size. Similar to other bat species, female nectar-feeding bats should increase their energy intake after parturition to meet the energy demands of offspring growth. However, previous studies have shown that nectar-feeding bats differ from other similar-sized bats in having a much higher metabolic rate. Therefore, I examined how nectarivorous bats respond to the energetic challenge of reproduction. In this study, the daily energy intake of pregnant and lactating Glossophaga soricina was measured during a 6-week period prior to and a 10-week period after parturition. Body mass of G. soricina increased linearly until parturition. Within the same time period, daily flight time decreased and daily energy intake remained constant. Probably, the reduced flight activity of pregnant bats compensated for the increased power requirements of flight, thus resulting in an almost constant daily energy turnover. During 35 days after parturition, neither flight time, body mass nor daily energy intake of lactating females changed significantly. On average, the daily energy intake of pregnant, lactating or non-reproducing G. soricina was not significantly different. Possibly, for unknown reasons, female G. soricina maintain a daily energy intake of a constant high level during and beyond reproduction.

Intraspecific scaling of flight power in the bat Glossophaga soricina (Phyllostomidae).

Aerodynamic theory predicts that power output during flight should vary with body mass by an exponent of 1.56 when wing morphology remains constant (within an individual), and by an exponent of 1.19 when wing morphology changes with body mass (within a species or between species). I tested these predictions by estimating the power input during horizontal flight in three pregnant and two subadult Glossophaga soricina using a multivariate regression model. This analysis yielded power input during resting and flight as well as the energetic equivalent of change in body mass. A comparison of the estimated flight power for pregnant G. soricina, with published data on flight power of nonpregnant adults, revealed that energy turnover in flight is highest for pregnant G. soricina. Flight power of a 13-g pregnant G. soricina was even higher than that of a 16-g non-pregnant Glossophaga longirostris. A least-squares regression analysis yielded the following equations for the intraspecific scaling of flight power with body mass: power input during horizontal flight (Pf) = 24099 body mass (bm; kg)2.15 (r2 = 0.97) for the intra-individual allometry (pregnancy) and Pf = 113 bm(kg)0.95 (r2 = 0.99) for the inter-individual allometry (ontogeny). Both mass exponents are not significantly different from the predicted values for the scaling relationship of flight power within an individual (1.56) and within a species (1.19). This is the first measurement of power input during flight for subadult and pregnant bats.

Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae: Glossophaginae) and its scaling in moths, birds and bats.

Three groups of specialist nectar-feeders covering a continuous size range from insects, birds and bats have evolved the ability for hovering flight. Among birds and bats these groups generally comprise small species, suggesting a relationship between hovering ability and size. In this study we established the scaling relationship of hovering power with body mass for nectar-feeding glossophagine bats (Phyllostomidae). Employing both standard and fast-response respirometry, we determined rates of gas exchange in Hylonycteris underwoodi (7 g) and Choeronycteris mexicana (13-18 g) during hover-feeding flights at an artificial flower that served as a respirometric mask to estimate metabolic power input. The O2 uptake rate (VO2) in ml g-1 h-1 (and derived power input) was 27.3 (1.12 W or 160 W kg-1) in 7-g Hylonycteris and 27.3 (2.63 W or 160 W kg-1) in 16.5-g Choeronycteris and thus consistent with measurements in 11.9-g Glossophaga soricina (158 W kg-1, Winter 1998). VO2 at the onset of hovering was also used to estimate power during forward flight, because after a transition from level forward to hovering flight gas exchange rates initially still reflect forward flight rates. VO2 during short hovering events (< 1.5 s) was 19.0 ml g-1 h-1 (1.8 W) in 16-g Choeronycteris, which was not significantly different from a previous, indirect estimate of the cost of level forward flight (2.1 W, Winter and von Helversen 1998). Our estimates suggest that power input during hovering flight Ph(W) increased with body mass M (kg) within 13-18-g Choeronycteris (n = 4) as Ph = 3544 (+/- 2057 SE) M1.76 (+/- 0.21 SE) and between different glossophagine bat species (n = 3) as Ph = 128 (+/- 2.4 SE) M0.95 (+/- 0.034 SE). The slopes of three scaling functions for flight power (hovering, level forward flight at intermediate speed and submaximal flight power) indicate that: 1. The relationship between flight power to flight speed may change with body mass in the 6-30-g bats from a J- towards a U-shaped curve. 2. A metabolic constraint (hovering flight power equal maximal flight power) may influence the upper size limit of 30-35 g for this group of flower specialists. Mass-specific power input (W kg-1) during hovering flight appeared constant with regard to body size (for the mass ranges considered), but differed significantly (P < 0.001) between groups. Group means were 393 W kg-1 (sphingid moths), 261 W kg-1 (hummingbirds) and 159 W kg-1 (glossophagine bats). Thus, glossophagine bats expend the least metabolic power per unit of body mass supported during hovering flight. At a metabolic power input of 1.1 W a glossophagine bat can generate the lift forces necessary for balancing 7 g against gravitation, whereas a hummingbird can support 4 g and a sphingid moth only 3 g of body mass with the same amount of metabolic energy. These differences in power input were not fully explained by differences in induced power output estimated from Rankine-Froude momentum-jet theory.