Ecology, 85(1), 2004, pp, 220-230 © 2004 by the Ecological Society of America

REPRODUCTIVE ENERGETICS OF CAPTIVE AND FREE-RANGING EGYPTIAN FRUIT (ROUSEITUS AEGYPTIACUS)

CARMI KORINE,1,2,4 JOHN SPEAKMAN,3 AND ZEEV ARAD1

[Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel 'Mitrani Department of Desert Ecology, Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion 84990 Israel 3School of Biological Sciences, University ~f Aberdeen, TiIlydrone Avenue, Aberdeen ABU 2TZ, and Division of Energy Balance and Obesity, Rowett Research Institute, Aberdeen, AB24 935, Scotland, u.K.

Abstract. This study explored how a flying frugivorous , the Egyptian fruit ( aegyptiacus), meets the increased energy requirements of reproduction. This bat feeds on low-protein fruit, and females have bimodal polyestrous cycles that are rel­ atively long for a small mammal. We measured the energy and water balance of captive nonreproductive, pregnant, and lactating females, and of free-ranging lactating females, Our results indicate that females use more than one strategy to cope with the high energy demands of reproduction, These strategies may change according to the availability of food and reproductive status, The primary strategy near the end of pregnancy and at peak lactation was increased food consumption, In the laboratory, mean metabolizable energy intake (MEl) of pregnant and lactating females (271 and 360 kJ/d, respectively) increased by 35% and 80%, respectively, compared to that of nonreproductive females (200 kJ/d), At peak lac­ tation, energy intake measured by doubly labeled water averaged 350 kJ/d. During late pregnancy, water turnover rate (WTO) increased by 15-23% compared to that of nonre­ productive females. In the field, WTO at peak lactation was 44% higher than in captive lactating females, and milk production was estimated to be 22 ml.zd, Absolute resting metabolic rate (RMR) in late pregnancy was significantly lower than the RMR of nonre­ productive females, suggesting that a metabolic depression was used as a compensatory mechanism, Fat deposition was evident during the second pregnancy, when food availability was high, presumably in preparation for a second lactation period, Fetal tissue represented ~ 1,3% of the total energy assimilated during pregnancy, and the gross efficiency oflactation averaged 24%. Both values are lower than the values reported for other eutherian , but similar to estimates for other bat , and probably reflect the high energy costs associated with flight. A long lactation period may be constrained by flight and the low­ protein diet of fruits, We conclude that the energy costs of Egyptian fruit bats during reproduction are distributed over a relatively long time, similar to those observed in large mammals. Key words: Egyptian fruit bat; energy balance; fat stores; lactation efficiency; Megachiroptera; metabolic depression; reproductive energetics; Rousettus aegyptiacus; water balance,

INTRODUCTION As a group, bats have several characteristics unique; among mammals with respect to their reproduction and' Several different physiological and behavioral strat­ life histories. They are typified by having long lW' egies for accommodating the increased energy demands spans for their body sizes, and most species give birth of reproduction have been identified in mammals, to a single offspring followed by extended parental car These strategies include increases in energy intake (Kunz and Pierson 1994). Moreover, pups do not begi (e.g., Brody 1945, Randolph et al. 1977, Millar 1978, foraging independently until they have nearly achieve, Hickling et al. 1991) or mobilization of fat reserves adult size, possibly due to the constraints of flight (Bar4 (Fedak and Anderson 1982) to fuel the increased de­ clay 1994). Consequently, pregnant bats may face high" mands, Alternatively, the increased requirements of re­ foraging costs because of the additional load of the, production can be offset by reduced physical activity embryo, and lactating bats are compelled to provisio~ (Randolph et al. 1977) or reduced maintenance energy their offspring for an extended period of time until they expenditure of the mother (Speakman and Racey 1987). can fly. Maternal investment of free-ranging bats (i.M' energy consumption and expenditure) has been studi~ mainly in insectivorous microchiropteran bats (Ku " Manuscript received 11 October 2002; revised 14 May 2003; et al. 1989a, b, 1990, Kunz et al. 1995, Stern et, accepted 20 May 2003,Corresponding Editor: S, J, Simpson, 1997, McLean and Speakman 1999), Several stud' 4 Present address: Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Midreshet Bcn-Gurion have shown that female microchiropterans incres 84990 Israel. E-mail: [email protected] their food consumption during reproduction (K' 220 MEGACHIROPTERAN BAT: MATERNAL INVESTMENT 221

74. Speakman and Racey 1987. Kurta et a1. 1989a. study, we focused on maternal reproductive effort of 90. Kunz et a1. 1995. McLean and Speakman 1999, the Egyptian fruit bat. Rousettus aegyptiacus (Mega­ , balds and Kunz 2000), whereas the use of fat stores chiroptera). This bat feeds mainly on fleshy fruits. es­ ese species appears to be of limited significance pecially of introduced figs (Ficus), which are low in eakman and Racey 1987. Kurta et al. 1989a, 1990. protein. The bats may also feed on leaves when fruit cLean and Speakman 1999). Speakman and Racey availability is very low. but not during the reproductive 987) and Racey and Speakman (1987) demonstrated cycle (Korine et al. 1999). In Israel, females have a at-the daily energy expenditure of three insectivorous bimodal polyestrous cycle. with a single young being 'at species did not increase between pregnancy and born after a four-month pregnancy in early spring actation, and suggested that females of these species (March-April) and in late summer (August-Septem­ , y compensate for the high energy costs of repro­ ber) (Makin 1990). The offspring are totally dependent ,bction by entering daily torpor. on their mothers for the first six weeks of life. Peak .Direct observations of torpor use by reproducing bats lactation occurs after six weeks, when the young de­ ave proved contradictory. Daily torpor during preg­ velop their ability to fly. Thereafter, the offspring typ~ ancy, lactation. and postlactation was not observed in ically follow their mothers to the feeding sites until her little brown bats, Myotis lucifugus (Kurta et al. weaning occurs at three months of age. At peak lac­ 1987; but see Burnett and August 1981), or big brown tation. R. aegyptiacus produces milk that contains rel­ 'bats. Eptesicus fuscus (Audet and Fenton 1988, Ham­ atively low fat, dry matter. and energy contents (Korine ilton and Barclay 1994, Grinevitch et al. 1995. Lausen and Arad 1999). and Barclay 2002). However. torpor was used by north­ Our goal was to determine how female R. aegyptia­ ern pipistrelle bats, Pipistrellus subfiavus (Winchell and cus meet the increased energy requirements of repro­ ii

ium sys­ .vals: 1.5,24, 48, and 96 h. Each bat was held separately productive, pregnant, and lactating females s calcu­ ,',during the first 24 hours, and samples were processed tured using mist nets as they emerged for nigbtl~:a

~ exper­ .Degen et al. (1981). The calculated mean TRW was USA) and injected subcutaneously with doubly labeled er-Con­ ompared to the mean TBW measured by drying three water containing 0.05 mL of 0.25 u.Ci/rnl, 3H (NEN30, .ecticut, rpses (two males and a female) to a constant mass Medical Research Products, Boston, Massachusetts, . rectum 60°C. USA) and 0.15-0.2 rnL 97% enriched 180 (ENRITECH, )couple Rehovot, Israel). Each female was then placed in a 'Field methods: Changes in body mass during the er (TH­ darkened cage for 80-120 min to allow for equilibra­ bimodal annual reproductive cycle \ll tem- tion of the markers with TBW. A sample of blood was We captured females at different reproductive stages then taken from the wing vein and divided into 5-6 ''follow the annual-cycle changes in body mass. Body lO-f.LL aliquots in 20-f.LL glass capillary tubes for l80 ., s for each female was measured at dusk when bats analysis, and into 2-3 60-f.L glass capillary tubes for e leaving the cave to visit the feeding sites. Makin 3R analysis. The capillaries were immediately sealed '~O) defined the periods of pregnancy, birth, and lac­ with a torch. After the initial blood sampling, females "on in each of the two annual reproductive cycles of were released. Samples of blood from five nonrepro­ egyptiacus. Using his criteria, the captured females ductive, five pregnant, and five lactating females were e"grouped according to the different stages of re­ taken, without injecting doubly labeled water, to de­ WTO)r ~Jlction. termine background levels of the isotopes. gy and] fee stages of pregnancy were defined: first, sec­ Each experiment lasted four consecutive days. The ~xpetiti ';::and third trimesters. Because the definition was first and second days were dedicated to marking and Jfatio# 'rpn gentle palpation, it was possible that some injection of individuals, and the following days (start­ 1988 ",'iearly pregnancy were missed. Three stages of ing on the second day) were dedicated to recapturing 'idu 'flwere defined, following Makin (1990) and the marked individuals. Each recaptured bat was mea­ mL ,alld Arad (1999): beginning, peak, and late. sured for morphological parameters and a second blood BN3 .,\~ .captured with attached young with forearm sample was collected. ~r~f :::::46 mm were classed as being at the be­ The capillaries containing samples for [80 analysis t, of lactation. Peak lactation was defined as (1) were kept in a refrigerator until analyzed using the ''\'captured with a pup that had a forearm length guanidine hydrochloride technique (Speakman 1997), }:'mtn, or (2) females captured without an off­ and the enrichment of the 180 was determined using a ~ .put with highly developed mammary glands mass spectrometer (VG Optima, Micromass, Man­ '~ld~d milk easily and with a bald area surround­ chester, UK). The rate of CO 2 production (in millimoles ~!f,~nd soft nipples. In contrast, females that were per day) was calculated according to Lifson and "tnd of the lactation period, defined as "late," McClintock (1966): JPkcn mammary glands from which only small RC0 = N12.08 tK; - K ) - 0.0l5K $',:of milk could be expressed. These mothers 2 d dN y'C, hard nipples, around which there was often where N is the number of moles of body water, and K;

"wn hair. and K d are the slopes of biological elimination of l80 tll hurting the nipples or scaring the mother and 3R, respectively. The term 0.015KdN is a correction " her pup, females'caught with a pup in the factor for the fractionation of the. markers. ~~ighed with their pup. To assess body mass The energetic equivalence of each milliliter of CO 2 her' alone, we separately captured 70 females produced was determined from the average chemical pfrps of various sizes. We separated mother composition of the fruits eaten by the bats during the hrefully and measured the forearm length and study (Korine et a!. 1999). An average fruit contained irtass of the pups. A significant correlation 75.9% water, 20.2% sugar, (L6% fat, 1.2% protein, and fshed between forearm length and body mass 2.3% fiber. The energy contents of I g of sugar, fat. (r2 = 0.96, P < 0.001), and the equation protein, and fiber are 17.7,39.5,23.6, and 6.3 kJ, re­ m this relationship was used to calculate the spectively (Robbins 1983). For our calculations, we 'e mother alone by measuring the forearm assumed that the digestibility of sugar, fat, and protein 'h,er pup and subtracting the predicted pup is 95% (Robbins 1983), and that fiber was not digested. :from the combined mass of mother and pup. About 4% of the energy is lost in the urine (Grodzinski <:,.i, ~: ' and Wunder 1975); thus, 1 g of fruit contains 4.2 kJ "'labeled water (DLW) measurements total energy, 3.9 kJ digestible energy, and 3.7 kJ met­ ,riments were conducted in the Barna Cave abolic energy, Assuming that I g of metabolized sugar, ount Carmel National Park (32°40' N, fat, and protein are equivalents of 830, 1400, and 862

: the northwestern part of Israel. Nonre­ mL CO 2, respectively (Robbins 1983), then I L CO 2 224 CARMI KORlNE ET AL.

TABLE 1. Mean (:t I SD) dry matter intake, apparent digestibility, gross energy intake (GEl), digestible energy intake (DEI), apparent energy digestibility of the dry matter, and metab­ olizable energy intake (MEl) of nonreproductive, pregnant, and lactating Egyptian fruit bat females maintained on a sycamore fig fruit diet.

Pregnant Nonreproductive nonlactating Lactating Energy measures (n = 3 females) (n = 5 females) (n = 5 females) Dry matter intake (g/d) 15.31 :t 1.65' 21.74 :t 0.75 b 26.72 ± 0.88' Apparent dry matter digestibility (%) 95.46 :t O.4Jb 92.03 :t 1.55' 96.44 :t 0.46' GEl (kJ/d) 219.75 :t 14.01' 07.00 :t 5.86b 90.65 :t 15.20' DEI (kJ/d) 208.71 :t 24.05' 82.23 :t 14.54b 75.52 :t 12.97' Apparent energy digestibility (%) 94.08 :t 0.97b 91.95:t 1.48' 96.17 :t 0.50' MEl (kJ/d) 200.36 :t 23.09' 70.94 :t 13.96b 60.50 :t 12.45' Notes: Different superscripts within a row indicate significant differences (P < 0.05). MEl was calculated assuming that the energy loss in the urine is 4% of the digestible energy intake (Grodzinski and Wunder 1975). produced is equivalent to 20.1 kJ metabolic energy and higher in lactating females than in nonreproductive and 20.93 kJ digestible energy. The energy expenditure cal­ pregnant nonlactating females, respectively (Table I). culated by the DLW technique does not include the Body temperature did not vary between females of energy exported as milk (Kurtaet al. 1989a). different reproductive status (Table 2). Mean metabolic rate (MR) during rest was significantly lower in preg­ Statistical analysis nant females than in nonreproductive (by 19%) and ' Comparisons between nonreproductive, pregnant, lactating females (by 23%) (Table 2). It is important and lactating. females were made using one-way AN-' . to note that this was a reduction in absolute,'rather than OVAs. The effect of external factors' on the metabo­ mass-Corrected,' metabolicrate and therefore was not lizable energy intake of free-ranging females was eval­ an indirect consequence of the increased mass of fe­ uated using multiple regression analysis: Comparisons males during late pregnancy. This decrease in preg­ between laboratory and field results of lactating fe­ nancy contrasted with the pattern of dry matter intake males were tested using Student's t test. Results are and energy intake (Table 1). Mean MR was not sig­ presented as meansrr 1 SD. A value of P < 0.05 was nificantly different between nonreproductive and lac­ accepted as significant. All analyses were performed tating females (Table 2), despite the fact that MEl of using SYSTAT 7.0 (SPSS 1997). lactating females was 80% higher than in nonrepro­ ductive females (Table 1). Consequently, MR was not RESULTS correlated with either DEI (P > 0.28) or MEl (P > Dry matter intake (DMI) and apparent dry matter '0.27). . digestibility (ADMD) varied significantly between bats Total body water (as percentage of body mass) was of different reproductive status. DMI during pregnancy highest in lactating and in pregnant females during late was 42% higher than in nonreproductive females, and pregnancy and differed significantly from that of fe­ in lactating females it was 74% and 23% higher than males in other stages of reproduction (Table 3). Water in nonreproductive and pregnant nonlactating females, turnover (WTO) differed significantly between the var­ respectively (Table 1). Gross energy intake (GEl), di­ ious stages of reproduction: It increased from the non­ gestible energy intake (DEI), and apparent energy di­ reproductive stage to pregnancy and peaked in lactating gestibility (AED) also differed significantly between free-ranging females. However, WTO did not differ females at different stages of reproduction. Metaboliz­ between females in mid-pregnancy in the laboratory able energy intake (MEl) was 35% higher in pregnancy and free-ranging lactating females (Table 3). WTO also than in nonreproductive females, and was 80% and 33% did not differ significantly between nonreproductive,

TABLE 2. Mean (:t 1 SD) body mass, body temperature (Tb) , and metabolic rate (MR) during the resting phase (12 h) of nonreproductive, pregnant, and lactating Egyptian fruit bat females maintained on a sycamore fig diet.

Status of females Body mass (g) MR (kJ/12 h) Nonreproductive (n = 3) 126.96 :t 11.08" 36.10 :t 0.96 44.69 :t 2.14" Pregnant nonlactating (n = 5) 154.52 :t 3.21 b 35.48 ± 0.51 36.14 :t 5.58 b Lactating (n = 5) 127.85 :t 6.37' 35.82 :t 0.39 47.16 :t 2.77' Note: Different superscripts within a column indicate significant differences (P < 0.05). MEGACHIROPTERAN,BAT: MATERNAL INVESTMENT 225

LE 3. Mean (:!: 1 SD) body mass, total body water (TBW), water turnover (WTO), and the ratio between WTO and TBW '~f Egyptian fruit bat females of different reproductive stages, maintained on a mixed diet. +;" . Status of females Body mass (g) TBW (%) WTO (ml.skgrt-d") WTO/TBW (%)

nceproductive female (n = 6) 118.5 :!: 6.9 c 70.5 :!: 6.4 b 718.6 :!: 125.9' 101.5 :!: 9.9 'y-mid pregnancy (n = 6) 137.4 :!: 6.5 b 76.2 ± 3.6 b 890.6 ± 67.9'" 117.1 ± 9.3 ', of pregnancy (n = 6) 160.1 :!: 3.8' 75.6 :!: 8.9'b 828.7 :!: 67.4 bc 110.9 ± 15.0 "Jb-Iactating (n = 6) 132.6 ± 9.0 b 69.8 ± 6.5' 707.4 ± 144.6c 102.9 :!: 28.5 fhe-ranging lactating (11 = 6) 130.3 :!: 9.5 b 79.8 ± 3.7' 1032.2 ± 191.3' 128.9 :!: 22.3 ,', Notes: Different superscripts 'within a column indicate significant differences (P < 0.05). "Lab-lactating" females are ~lriales that produced milk but were separated from their offspring and were not milked manually. Pregnant females were ,not lactating. TBW was calculated in milliliters and is presented as percentage of body mass - [TBW (%) = 100(TBW/ :l\l.)]. WTO was calculated in mUd and is presented in mL·kg-l·d-1 for comparison with other mammals.

lId-of-pregnancy, and lactating females measured in experimental groups, the ratio between WTO and TBW y laboratory (Table 3). These females were manually exceeded 100% (Table 3). ,'lked, however, and our milking efforts probably did Overall, 310 females in various stages of reproduction ot compare with the milking process in nature. The were captured. Females that were neither pregnant nor ~ and :tlifference in WTO between free-ranging lactating fe­ lactating (NRF) were captured year round, but mainly e 1). .males and lactating females in the laboratory can prob­ between October and December. From December to es of /4~ly be attributed to activity differences and to differ­ April (first pregnancy cycle), pregnant females were cap­ xrlic ;~nces in the actual extent of "lactation. In all of the tured in various stages of pregnancy: BPI, beginning of ireg­ '} and -tant 180 36, 24 than not . fe­ 160 14 reg­ take 140 sig­ § lac­ en ~ 120 [ of .D. Q) oro­ (ij not E 100 ) > 2 0 -en 80 vas en ell late E 60 fe­ >­ -0 0 Iter m 'ar­ 40 m­ ing 20 fer iry 0 Iso NRF BPI MPI EPI BU PU EU EU& BPII MPII EPII BUI PUI EUI ve. BPII c ~ c "S "S "S Ol a. t> > o -,03 co 0.. -,::J -, -, -, ::J Ql 0 Ql ~ ~ I I I « en 0 z 0 I I I c c c I I , o c 1 .!. C a. ..L ..L Ql 03 ~ ::J ::J ::J Ol (I)' o o 03 ~ C. -, -, -, ::J ::J 0 -, « ~ -, « en 0 0 Reproductive stages

FIG. 1.{ The annual cycle of body mass (mean + 1 SD) of free-ranging female Egyptian fruit bats: NRF, nonreproductive females; BPI, beginning of pregnancy I; MPI, mid pregnancy I; EPI, end of pregnancy I; BLI, beginning of lactation I; PLI, peak lactation 1; ELI, end of lactation I; ELI + BPII, end of lactation I and beginning of pregnancy II; BPII' beginning of pregnancy II; MPII, mid pregnancy II; EPII, end of pregnancy II; BLII, beginning of lactation I; PLI1, peak lactation II; ELII, end of lactation II. Numbers above the bars represent sample sizes. All values for lactating bats are values of mothers without their pups (see Methods). 226 CARMI KORINE ET AL.

TABLE 4. Mean (± I SD) body mass, daily carbon dioxide production, and the digestible energy intake and metabolized energy intake equivalents of free-ranging, lactating female Egyptian fruit bats in comparison to balance measurements in the laboratory.

Field results Laboratory Energy measures (ll = 6) results (ll = 5) P Body mass (g) 130.3 ± 9.5 127.3 ± 7.2 NS Carbon dioxide production (Lid) 17.4 .± 3.4 Digestible energy intake (kJ/d) 363.4 ± 71.2 375.5 ± 13.0 NS Metabolized energy intake (kJ/d) 349.4 ± 68.4 360.5 ± 12.4 NS

Note: Rates of CO2 production were only measured in the field. pregnancy; MPI, mid-pregnancy; and EPI, end of preg­ pregnant, and 41 were lactating mothers. Unfortuna nancy (Fig. 1). From April to the beginning of August, ly, despite this field effort, only lactating females weri lactating females (first lactation cycle) were captured in recaptured and their recapture success was only 15%.. various stages of lactation: BLI, beginning of lactation; The body mass of lactating females did not differ sig; PLI, peak lactation; and ELI, end of lactation (Fig. 1). nificantly between capture and recapture 133.3 ::t:: 9.5. Fat accumulation can be estimated by comparing body g and 128.7 ::t:: 7.5 g, respectively (n = 6, t = 0.33, pi masses of either nonreproductive females vs. females at > 0.3). The mean time interval between capture and') the beginning of lactation, or females at the beginning recapture was 1.63 ::t:: 0.51 d. of lactation vs. the peak of lactation. These comparisons A multivariate stepwise regression analysis between'. did not reveal significant differences, and suggest lim­ MEl of free-ranging lactating females and body mass,. ited use of fat reserves during the first cycle of lactation. percentage of body mass change, time lapse between' Of ELI-defined females, 84% were also pregnant in the captures, and ambient temperature revealed no signif­ second pregnancy cycle (ELI + BPII). Comparison of icant correlations (F = 1.21, P > 0.58). The lack of'. body mass of PLI and ELI females did not reveal sig­ correlation indicated that the measurement did not af- ', nificant differences between the two groups. However, feet the energy. consumption oflactating females. Com­ significant differences were fd.~ndbetween the body parison of th(:\~ody mass of lactating females and di­ masses of females at the end Of 'lactation i and at the gestible and metabolized energy intake did not reveal beginning of pregnancy of the second reproductive cycle significant differences between field and laboratory re­ (ELI + BPII and ELI females) (( = 5.48, df = 39, P < sults (Table 4). 0.0001), and between the body masses of ELI + BPII and PLI females (t = 10.12, df = 46, P < 0.0001). Body DISCUSSION mass of the ELI + BPII group was also significantly Gestation higher than that of the BPI (t = 5.62, df = 51, P < 0.0001) and BPII animals (t = 3.61, df = 38, P < In the present study, energy intake of pregnant fe­ 0.0001). These comparisons suggest that the increase in males was increased by 35% compared to that of non­ body mass of ELI + BPII females was a result not only reproductive females. A similar increase in energy in­ of the second pregnancy, but also of the accumulation take during pregnancy compared to nonreproductive of body reserves. females has been observed in several species of rodents The second pregnancy cycle extended from May to (Microtus arvalis, 32%, Migula [1969]; Sigmodon his­ September. No significant differences were found in pidus, 25%, .Randolph et al. [1977]; Phodopus sun­ body mass between the two pregnancy. cycles (for each gorus, 33%,Weiner [1987]). Female Rousettus aegyp­ stage, not including the ELI + BPlIgroup; Fig. 1). The tiacus used an additional strategy to cope with the in­ second lactation cycle continued from September to Oc­ creased energy demands during pregnancy. We ob­ tober (BLlI, PLII, and ELII). The body mass of PLII served that resting metabolic rate was 19% lower in females was significantly lower than that of nonrepro­ pregnapt that in nonreproductive females. We suggest ductive females (t = 3.42, df = 61, P < 0.0001), sug­ that this reduction in resting metabolism during ges­ gesting the use of body reserves during the second lac­ tation may act as a compensatory mechanism, as pre­ tation cycle, consistent with the increase in body mass viously proposed by Speakman and Racey (1987). The in the ELI + BPII group. From the beginning to peak decrease in metabolic rate of pregnant females during of lactation, body mass decreased significantly (t = 2.86, the resting phase may enable them to spend more time df = 59, P < 0.04), possibly indicating the prolonged in other activities such as foraging (Korine et al. 1994), energetic stress endured by females at the PLII stage. or potentially to allocate more energy to fat storage or This pattern differed from the pattern of the first lactation milk production. It was also reported that female com­ cycle, when body mass did not change significantly. mon blossom-bats, australis (small Me­ We captured 113 females for the DLW measure­ gachiropteran bats), use daily torpor during pregnancy ments. Of these, 26 were nonreproductive, 46 were (Geiser et al. 2001). However Voigt (2003) did not find MEGACHIROPTERAN BAT: MATERNAL INVESTMENT 227

vidence that captive female glossophagine bats annual cycle of body mass. Both phenomena suggest .rpor or hypothermia during pregnancy or lacta­ diminishing fat reserves at the end of the bimodal re­ production cycle. In contrast to our findings, micro­ ling pregnancy, female R. aegyptiacus increased chiropteran insectivorous bats do not store fat to sup­ ibody mass in preparation for the high energetic port lactation (Racey and Speakman 1987, Kurta et al. 'of lactation. This conclusion is supported by our 1989a, McLean and Speakman 1999, Reynolds and 'rom the annual changes in body mass. During the Kunz 2000; see also Voigt [2003] for female glosso­ regnancy cycle, evidence of mass accumulation phagine bats). This difference may reflect the low body ~!limited, because body mass did not differsignif­ masses of the insectivorous and glossophagine bats that ntly between females at the beginning of .lactation have been studied, relative to R. aegyptiacus, and the , ;nonreproductive females (assuming that mass loss scaling of potential fat storage and MR to body mass, he beginning of lactation equals the body mass of which makes fat storage a more feasible option in larger !:;newborn and the placenta). At this time of year, animals. re.is low fruit availability and the fruit that is avail­ Comparison of the two methods for estimating en­ cis of poorer quality (Korine et al. 1999). In con­ ergy intake during peak lactation (feeding trials in the r sig­ .it; during the second pregnancy cycle (April-May laboratory and DLW in the field) did not reveal sig­ ±: 9.5 .'July-August), significant differences in body mass nificant differences between the two sets of measure­ 33, P .'re found between females at the beginning of lac­ ments. This was unexpected, because estimates using ~ and ;tlltion and nonreproductive females (an average in­ food intake include energy exported as milk, whereas '~rease of 12 g), indicating fat accumulation in prepa­ estimates using DLW do not. Perhaps not all lactating ween i:,ration for the second lactation cycle. This occurs at the females captured in the field were at peak lactation, nass, 'itfue of year when food availability and quality are high which was reflected by the large range in values for veen i'(Korine et al. 1999). ' body mass (121-142 g) and metabolic energy expen­ gnif­ :e(1 'The energy content of a newborn fruit bat was 108 diture (290-438 kJ/d). k of \kJ;with a dry mass of 5 g and energy content of 21.5 The mean energy expenditure of free-ranging lac­ t af­ \C~lg(Korine1996).Of the-energy .storedrin the fetus, tating females was 350 kJ/d. This value was 99% higher' 'om­ ;plitcenta, uterus, and mammaryiglands,,"':'78% is stored than'that:allometrically,predicted for-bats (Nagy et al. 1 di­ l~hhe fetus -itself {Kurta:lind :Kunz·:11987).Thus·, the 1999:,Eq,\4). Similar deviations.werereported for two veal :'f<>la1 energy production ofRiaegyptiacusduring,preg­ species-of microchiropterans at peak', 'lactation ,(80% I re­ 'nancy was 138.5 kJ (l08178:x 100),0i"3:46IkJ/d; as­ and 85%; Kurta et al. 1989a, 1990): It has been sug­ :suming that most of the growth and Investment.inthe gestedpreviously that the field metabolic rate (FMR) embryonic tissues occurs during the third trimester (40 is 'proportional to the metabolism at rest (RMR or days). Metabolizable energy intake in late pregnancy BMR), and that maximal FMR is ~4-7 times higher was 271 kJ/d; therefore, this tissue energy represents than the BMR (Speakman 1997). This ratio of BMR ~ 1.3% of the total energy assimilated during pregnan­ to energy expenditure for lactating R. aegyptiacus was fe­ cy. This value is similar to the values published for 5.4 (BMR of R. aegyptiacus was 66 kJ/d; Korine and on­ two microchiropteran species, 1.2% and 2% (Kurta et Arad [1993]), suggesting that these bats are operating in­ al. 1989a, 1990), and is substantially (42-56%) lower at the upper end of the range of maximal energy ex­ ive than reported values of other mammals during preg­ penditures during lactation. This figure is consistent nts nancy (McClure 1987).' Low energetic efficiency dur­ with the estimate of 7.0 X BMR reported for nonre­ lis­ ing pregnancy may be explained by the time allocated productive individuals of the megachiropteran bat Sy­ 'tn­ to flight and by the high energetic cost of flying. conycteris australis (Geiser and Coburn 1999). vp­ \ in­ Lactation Energetic cost offoraging .andforaging time Jb­ Metabolizable energyintake during peak lactation in during lactation in the laboratory was 80% higher than for nonreproduc­ The daily energy expenditure of the bats can be di­ est tive females. Similar increases in MEl have been re­ vided into three components: energy expenditure dur­ es­ ported for several rodent species (Sigmodon hispidus, ing the resting phase, energy expenditure when resting 'e­ 66%, Randolph et al. [1977]; Microyus sungorus, during the active phase (for R. aegyptiacus, while eat­ he 133%, Weiner [1987]; Peromyscus leucopus, 130%, ing fruits at a feeding station), and energy expenditure ng Millar [1978]; Neotoma fioridana, 101%, McClure during flight. The bats in the present study generally ne [1987]). McClure (1987) suggested that the extent of emerged from their day roosts 30 min after sunset, and f), increase is smaller in species that rely on fat accu­ returned to the roost within the last hour of the night or mutation. Following this argument, an increase of 80% (Korine et al. 1994). During the activity phase there n­ in the energy intake during peak lactation for R. ae­ were relatively few observations of bats returning to gyptiacus may indicate the use of fat reserves during the roost (Korine 1996). Thus, it can be assumed that :y this period. This is further supported by the high total there are two distinct phases: the resting and activity d body water of lactating females in the field and by the phases. During the lactation period in captivity, the 228 CARMI KORINE ET AL. Ecology, Vol. 85,'

~ light regime was 16L : 8D. Because the time allo­ yields 0.6, 1.07, and 0.4 g H20 , respectively; Rob' cated for flight and eating is not known for this species, 1983), and drinking water. Fruit bats drink an ave. we estimated it by using a formula suggested by Hel­ of 10 mL HP/d in the laboratory even when they £ vel'sen and Reyer (1984): P, X t + (8 ~ t) x POI + 16 on fleshy fruits (Korine 1996). Assuming that X Pde = MEl = 350 kI/d, where t represents time drink similar amounts of water in the wild, 140 g allocated for each activity per day, Pf is energetic cost an average fruit would fulfill the rest of the water in ~38. during flight, POI is energetic cost in the night roost, (124 mL H 20 ). Based on our laboratory work, and Pde is energetic cost in day roosts. of the mass of fleshy fruits (mulberry and sycamo P, can be estimated using the allometric equation fig) was Iostin fruit orts; on average, this would suggested by Thomas (1975) to predict flight costs of equivalent to harvesting 225 g of fruit. bats frum their body mass (W): P, = 50.2 W079, where The water output during lactation included evap P, is measured in kilocalories per hour (SI conversion: ration of water both during flight and during rest, wat 1 kilojoule = 4.184 kilucalories) and body mass is in loss through the feces and urine, and water loss throug kilograms.. This equation refers only to horizontal milk production. Water loss (evaporation, feces, urine flight, whereas bat flight in the field is more complex. at rest was calculated by changes in body mass of lac­ Helversen and Reyer (1984) suggested multiplying this tating females at peak lactation (without pups) between' value by 1.3. The corrected P, for a lactating R. ae­ capture at sundown and release at dusk. Overall, 19', gyptiacus female is 54.6 kIth. We calculated POI from lactating females were captured, and lost an average of l: the oxygen consumption of lactating females and mul­ 17.5 g of their body mass (M) during the resting period' tiplied by 2, as suggested by Noll (1979a), giving a (i.e., water loss during rest). The water loss during total of 7.86 kIth. Similarly, Par was calculated from flight was calculated using Carpenter's (1986) allo­ resting oxygen consumption to be 3.93 kIth. Using metric equation: water loss (in milliliters per kilogram these values in the equation results in: 54.6t + (8 - t) per hour) = 4.23M-o,602 (in kilograms). According to x 7.86 + 16 x 3.93 = 350 kI/d. Therefore, t for flight this equation, the expected water loss during 4.8 h of is 4.8 h. Thus, lactating females invest only 20% of flight for a fruit bat with a mean body mass of 130 g their time in flight, but the energetic cost of this flight would be 9 mL. The remainder of the water loss, during amounts' to 262 kJ (54.6 x 4.8), which is 75% of the rest and activity, was assessed from water evaporation total daily energy expenditure. This value is higher than measurements during the feeding experiments in the the cost of flight in lactating Myotis lucifugus (66%; laboratory, and was estimated to be 9 mL during 3.2 Kurta et aI. 1989a), and is at the very upper limit of h (Korine 1996). Assuming that fruits are eaten in a the range for insect- or nectar-feeding microchiropter­ similar manner in the laboratory and the field, water ans (38-74%; Kurta et aI. 1989b). loss through feces and urine was ~59.3% of the water loss during activity (Korine 1996); therefore, 79.5 mL Water turnover of lactating females of water are lost in feces and urine. Daily water export Mean WTO of free-ranging lactating R. aegyptiacus as milk production at peak lactation was ~ 134 - (17.5 females was 1032 mL·kg-1·d- 1. A broad range of values + 9 + 9 + 79.5) = 19 mUd. Daily water production was reported for various free-ranging bats. In nonre­ as milk can also be estimated from the difference in productive, nectar- and pollen-feeding megachiropter­ water turnover between lactating females in the field an S. australis, mean WTO was 1800 mL·kg-J·d-J (40 mUd) and females in the laboratory (which did (Geiser and Coburn 1999), whereas in the nectarivo­ not lactate). According to these calculations, 18 mL of rous microchiropteran Anoura caudifer, mean WTO water were lost during activity, and therefore the water was 1165 mL·kg-l.d- t (Helversen and Reyer 1984). output as milk predicted by this method was similar at WTO during peak lactation of Eptesicus fuscus, an in­ 22 mUd. A third method of estimating water transfer sectivorous rnicrochiropteran, was 939 ml.-kgv-d'" in milk is to evaluate milk transfer from offspring en­ (Kurta et aI. 1990). The differences in WTO between ergy demands. Noll (1979b) measured the oxygen con­ the species inay be attributed to habitat (dry vs. wet), sumption of R. aegyptiucus pups in captivity from 1 stage of reproduction, and type of food (insect, nectar, wk to 8 wk of age. According to his measurements, or fruit) consumed by each species. the daily energy consumption of a 6-7 wk-old pup Body mass of lactating females in the present study (corresponding to peak lactation in the field), ata body did not differ significantly between capture and recap­ mass of 50 g, was 110.8 kI/d. Because the mean energy ture. Thus, we can assume an equal output and input content of milk is 5.05 kIlg during peak lactation (Ko­ of water (Nagy and Costa 1980). The mean WTO of rine and Arad 1999), the estimated daily milk produc­ these females was 134 mUd. The water input consists tion would be 22 mUd, similar to our previous cal­ of water in food (mean water content in the fruits eaten culation. These values are 5% lower than the prediction by/bats during the reproductive period is 76%; Korine of Hanwell and Peaker (1977) and 46% higher than 1996), metabolic water production (0.126 g metabolic that of Oftedal (1984). Both allometric equations as­ water production for each gram of fruit, assuming that sume that the pup receives all of its energetic needs metabolism of 1 g of carbohydrates, fat, and protein from milk alone. MEGACillROPTERAN BAT: MATERNAL INVESTMENT 229

oss energetic efficiency of lactation the values reported for other eutherian mammals, Such low values can be attributed to high costs of flight and tgetic efficiency of milk production express­ the amount of time spent in flight when foraging. thof energy invested in the milk to the in­ 'J]ietabolic energy intake above maintenance ACKNOWLEDGMENTS ents. As already noted, measurements by the The Technion-Institute of Technology supported this study. ~linique do not include the energy exported as We thank Arnir Shechter, Aya Korine, and Chen Korine for 'A;ccording to our estimates, 22 g X 5.05 kJ/g their valuable help in the field, and Mrs. Shoshana Golden­ .~nergy berg and Mr. Peter Thomson for the technical assistance in content of the milk of R. aegyptiacus at the laboratory. l,\!Jta~ion; Korine and Arad [1999]) would yield Jed evapor;~ )daily milk energy output of 111 kJ/d. Hence, LtTERATURE CITED rest, waterl'';' J daily energy cost at peak lactation is estimated Audet, D., and M. B. Fenton. 1988. Heterothermy and the use of torpor by the bat Eptesicus fuscus (Chiroptera: Ves­ ISS througtiii~ ~. kJ/d (350 + III kJ/d), and the estimated en­ pertilionidae): a field study. Physiological Zoology 61: 197­ ces, urine)!) i!, efficiency of milk production at peak lactation 204. :ISS of 1ac-':,f' 4%. This value is lower than the estimated effi­ Barclay, R. M. R. 1994. Constraints on reproduction by flying ) between:;:~ cy values for lactation in other mammals (30-60%; .vertebrates-energy and calcium. American Naturalist 144: verall, 19:',; 8y' 1945, Fedak and Anderson 1982, Costa et al. 1021-1031. 1945. verage of.' .~).Jower Brody, S. Bioenergetics and growth. Hanfer, New than the range for microchiropteran in­ York, New York, USA. 19 period" ~~iivorous bats (28-32%; Kurta et al. 1989b, 1990), Burnett, C. D., and P. V. August. 1981. Time and energy S during iiFslightly higher than in a nectar-feeding bat (19%; budgets for day roosting in a maternity colony of Myotis ~6) allo­ oigt 2003). Low energetic efficiencies of milk pro- lucifugus. Journal of Mammalogy 62:758-766. .i10gram u,ction in bats may be attributed to the large amount Carpenter, R. E. 1986. Flight physiology of intermediate­ sized fruit bats (Pteropodidae). Journal of Experimental I'ding to ftime that they allocate to flight and its cost, which Biology 120:79-103. ' 1-.8 h of ~"~Y constrain the energy allocated to milk production. Chruszcz, B. J., and R. M. R. Barclay. 2002. Thermoregu­ f 130 g oreover, the need to carry a pup while foraging may latory ecology of a solitary bat, Myotis evotis; roosting in during rther increase the energetic .cost of 'flight during the rock crevices. Functional Ecology 16:18-26. Costa;' D. P., J. LeBoeuf, A. C. Huntley, and C. L. Ortiz. Jration ~t~tioh period in R. aegyptiacus, th~s reducing the l!~ici~ncy '1986. The energetics of lactation in the northern elephant in the of milk production...... , seal,Miroungaangustirostris, Journal of Zoology (London) 'lg 3.2 209:21-33. 11 in a Summary . Degen,A. A., B. Pinshow, P. U. Alkon, and H. Arnon. 1981. water Tritiated water for estimating total body water and water In agreement with our first prediction, we found that turnover rate in birds. Journal of Applied Physiology 51: Water increased food consumption is the main strategy of R. 1183-1188. 5 mL aegyptiacus to meet the increased energy requirements Ellis, W. A. H., T. G. Marples, and W. R. Phillips. 1991. The "port effects of a temperature-determined food supply on the during late pregnancy and peak lactation. Similarly, 17,5 annual activity cycle of the lesser long-eared bat, Nycto­ microchiropteran insectivorous females also increased 'tion philus geoffroyi Leach, 1821 (Microchiroptera: Vesperti­ their insect consumption during pregnancy and lacta­ lionidae). Australian Journal of Zoology 39:263-271. e in tion. Thus, females of both suborders use a similar Fedak, M. A., and S. S. Anderson. 1982. The energetics of ie1d lactation: accurate measurements from a large wild marn­ strategy to cope with the high energetic demands during did mal, the grey seal (Halicboerus gryypus). Journal of Zo­ the reproductive period. Evidence for mass accumu­ ~ of ology (London) 198:473-479. lation and its use to sustain the lactation period was Geiser, E, and D. K. Coburn. 1999. Field metabolic rates and Iter water uptake in the blossom-bat Syconycteris australis (Me­ . at evident only during' the second reproductive cycle, when fruit availability and quality were high. The use gachiroptera). Journal of Comparative Physiology B 169: fer 133-138. of fat reserves was not reported for microchiropteran n­ Geiser, E, G. Kortner, and B. S. Law. 2001. Daily torpor in insectivorous females, apparently due to their low body o- a pregnant common blossom-bat (Syconycteris australis: mass. In contrast to our third prediction, metabolic rate Megachiroptera). Australian Mammalogy 23:53-56. during the resting phase significantly decreased during Grinevitch, L., S. L. Holroyd, and R. M. R. Barclay. 1995. Sex differences in the use of daily torpor and foraging time late pregnancy. This suggests that a metabolic depres­ p by the big brown bats (Eptesicus fuscus) during the repro­ sion is used as a compensatory mechanism for at least ductive season. Journal of Zoology (London) 235:301-309. part of the reproductive cycle. Studies on microchi­ Grodzinski, W., and B. A. Wunder. 1975. Ecological ener­ ropteran insectivorous females provide conflicting getics of small mammals. Pages 173~204 in E B. Goley, views, and further studies on females from both sub­ K. Petrusewicz, and L. Ryszkowski, editors. Small mam­ mals: their productivity and population dynamics. Cam­ orders are needed. Our results indicate thatreproduc­ bridge University Press, Cambridge, UK. tive females use more than one strategy to cope with Hamilton, I. M., and R. M. R. Barclay. 1994. Patterns of the high energetic demands. These strategies may shift daily torpor and day-roost selection by male and female according to food availability and reproductive phase. big brown bats (Eptesicus fuscus). Canadian Journal of Zo­ ology 72:744-749. The gross energetic efficiencies of pregnancy and lac­ Hanwell, A., and M. Peaker. 1977. Physiological effects of tation in the present study (and in other studies of mi­ lactation on the mother. Symposium of the' Zoological So­ crochiropteran insectivorous females) are lower than ciety of London 41:297-312. 230 CARMI KORINE ET AL.

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