The short-nosed fruit bat, Cynopterus sphinx is a common plant-visiting bat that is widely distributed throughout the Indo-Malayan region. In this chapter, we discuss the dispersal patterns, mating strategy and genetic diversity in the short-nosed fruit bat C. sphinx. We used a broad-range of techniques, including mark-recapture, radio-telemetry and molecular biology analyses. Our studies uncovered unique aspects of the dispersal, mating system and genetic diversity of these bats. Both the sexes of C. sphinx were found to disperse completely from the natal harems before subadult stage and young female C. sphinx become members of a harem much earlier than their male counterparts. The nonharem males are reproductively active, gain access to harem females and sire more offspring in July–August breeding season than March–April breeding season and presumably obtain some reproductive success. Our molecular study shows that considerable genetic diversity was observed in this species from different zonal populations, possibly due to complete dispersal of juveniles of both the sexes from their natal groups and gene flow between the zones. All these studies suggest not only a predictive framework for future studies, but also the use of these data in the management and meaningful conservation of this species.
- Cynopterus sphinx
- fruit bat
- dispersal pattern
- mating strategy
- genetic diversity
1. Introduction - Study species
The Indian short-nosed fruit bat,
These bats use several types of diurnal roosts and are known to alter different types of foliages (palm and mast trees) to construct tents and attract females (Figure 2a and b) [2, 4, 5, 6]. Although different types of altered plant structures are referred to as bat tents , the first account of tent making by a male bat came from observations on
2. Dispersal patterns
Displacement of a juvenile from its birth place to the first site of reproduction is termed as natal dispersal . This natal dispersal is one of the factors contributing to the central evolutionary forces that affect the natural populations. Also, it is the key life history trait that is involved in both species persistence and evolution . Understanding the patterns of dispersal is important in population ecology and conservation biology [17, 19]. Bats are known to exhibit varying degrees of dispersal and philopatry based on their social system [20, 21]. The short-nosed fruit bat
2.2 Materials and methods
In order to understand the dispersal pattern in
2.3 Results and discussion
Our results showed that female proportion in harem increases considerably from pups to subadults. Both the sexes are equal in number (1:1) in the pup stage, whereas the sex ratio was female biased in the juvenile (1:1.8) and subadult stage (1:4.2). In mammals, dispersal is usually male biased and this also holds true for most bat species studied to date [17, 22, 23]. However, several studies on tropical species indicate that there may be cases where females also disperse . Our study suggests that the juveniles of both the sexes disperse from their natal group before entering the subadult stage. We mostly captured dispersed juveniles and harems in which post-lactating females were present without the young ones. In many of the day roosts, the number of juvenile bats were disproportionate to the number of post-lactating females, especially when the juvenile bats were predominant.
The capture rate of juvenile females outnumbered the juvenile males, which suggest that the males dispersed early from the natal roost. One could suggest that maternal neglect could be playing a strong role in the altered sex ratio in
In accordance with the general mammalian pattern the females of most group-living bats, including some harem-forming species and all temperate zone species, are strongly philopatric which includes evening bat
In this study, the female proportion in harems increases considerably from pups to subadults. Compared to juveniles (1:1.8), sex ratio was highly skewed towards females in the subadult stage (1:4.2). From the total of 52 subadults, only 10 were males. Moreover, not a single subadult male bat was found to be roosting in a harem. This explains that the males disperse from the natal roost before subadult stage. From the 42 captured subadult females, it was observed that four subadult females were pregnant showing that the females matured earlier and were engaged in reproductive activities during the subadult stage itself. Lower rate of juvenile survivorship maybe one of the reasons for the low capture of adult males , which remains unclear. The probability of censusing these bats remain low because the male bats preferred to roost in dense, unmodified and previously unoccupied foliages. During the capture, the number of subadult females were larger as they joined established harems, formed a new harem of subadult females with an adult male or they remained alone in the roost.
However, we were not able to find out whether the dispersed juvenile bats return back to their natal harems. The probability of making local migrations even during the breeding season is rare in both
We identify that young female
3. Mating strategy
Factors responsible for the occurrence of nonharem males and mechanisms used to acquire harem male status.
Polygynous mating is one of the most salient features of mammalian social structure and has potentially far-reaching consequences for a diverse array of evolutionary processes . Male reproductive success in polygynous mammals is largely attributed to the spatial and temporal patterns of female aggregation [43, 44]. Receptive females are reliant on variation in resource distribution, predation pressure, costs of social living and activities of males . One of the major factors that affect the mating success of resource-based polygynous mating animals is the resource distribution. Females choose males indirectly by mating with males that defend the highest quality resource when the males control access to the resources that these females require for reproduction . Males that can make the greatest genetic contribution to the fitness of their offspring are chosen by the females .
Bats exhibit various forms of mating behavior ranging from simple monogamy to resource and female defense polygyny, as well as leks [46, 47]. Among these, resource defense polygyny is the most commonly observed mating pattern . Bats establish a harem by defending critical resources such as food, shelter or mates . Males potentially gaining favored access to several females is considered as one of the main benefits in resource defense polygyny and a healthy male inseminates the females [43, 46]. It is observed that several Neotropical fruit bats such as
If this is true, what is the role of such nonharem males in the population or colony? What are the factors that cause the occurrence of nonharem males in a colony of
3.2 Materials and methods
The study involves understanding the mating status of solitary males, bat captures were confined to day roosting places. Captures at roosting places indicated whether a male was solitary or a harem holder. Every week, we inspected trees and censused day roosts regardless of the number of incumbents (solitary or harem). Roosting groups with a single adult male with one or more adult females were considered as harems . However, apart from such successful males, a number of adult males were also observed roosting solitarily. All the individuals of harems and the solitary males, which roost adjacent to the harems, were captured just before emergence using a hoop net with an extensible aluminum pole.
All the bats of harem groups and nonharem males were tagged with a color-coded bead necklace. We used beads of ten different colors, each color denoting a number from 0 to 9. We loaded each necklace with 1–3 beads. Thus, there were 999 possible sequential arrangements of the color beads. We have used this type of tagging for various studies and have observed no apparent detrimental effects on bats. After marking, all individuals were released at the site of capture. These color coded bead necklace markings allowed us to identify individuals and determine their previous roosting locations. The census, mark-recapture and radio-telemetry studies data were used to assess the reproductive condition, mobility, roosting pattern and status of adult males (harem/nonharem).
3.3 Results and discussion
One of the striking features of tent-making male bats is that they use tents as a resource to recruit large numbers of females and copulate with them [46, 51]. Although experimental evidence supporting causal factors for resource-defense polygyny is lacking, scarcity of resources is thought to be one of the factors for aggregation of females . Solitary roosting existence of some adult males is one of the main consequences of resource-defense polygyny as the males fail to defend a resource. We attempted to study the resource-defense polygyny in
Our results suggest that the male success in female recruitment was not due to shortage of tents. We found that, nearly 39% of adult males were roosting alone. This observation was based on >90% of nonharem males roosting adjacent to harems and also 50% of nonharem males had scrotal testes. In addition, the mark recapture study showed that the transition status of males from nonharem to harem was possibly due to previously unobserved mode and the female recruitment is associated with resource (roost). It indicates that the solitary males are involved actively in female recruitment to their roosts and also in the process of mating. During our study we observed that many solitary males recruited females within a short period of time. A nonharem male’s effort to gain access to adult female cannot be hindered by the solitary nature
The mode of attaining harem male status differs from species to species. For e.g. young males of
However, subordinate manakin males readily take the place of the dominant males in order to obtain a long term benefit from the association. Subordinate males’ relationship with dominant males adds an extra benefit to the subordinate males by increasing the inclusive fitness thereby leading to higher reproductive output . Our efforts to identify the morphological differences between harem males and nonharem males were not successful as we did not find substantial differences in the forearm length and body mass. This is surprising because an individual’s body condition is often the most important determinant for alternative mating tactics [67, 68]. Larger and heavier males are typically dominant in male–male contests and reproduce more often . In male common shrews
Individuals with territory and resource, typically have a higher reproductive success than the males without territories due to strong competition for mates in a polygynous mating system. Males with territories usually monopolize and probably fertilize many females . The males which does not possess any territory follow alternative mating strategy either as satellites [72, 73] or as sneakers [74, 75]. Similarly, among polygynous bats such as
The roosting preference of females seems more likely to increase the chances for nonharem males fertilizing some of the females. Apart from the mating success of nonharem males, low paternity for harem males can also occur as a result of female choice.
Similarly, pallid bats
In the Bechstein’s bat
During July and August, the frequency of nonharem males were found to be highest. Timing of sexual maturity of young males might be a probable reason, though no reports on timing of sexual maturity of young male bats in southern India. Reports from central India suggest that males born during the June–July parturition and February–March parturition were able to mate during September–October of the following year . The number of nonharem males censused during August to October was relatively high in the study area. This can be attributed to the competition among first time breeding males to establish a day roost to recruit females before securing mating in October–November.
Our radio-telemetry observations suggest that females aggregated with a solitary male. Interestingly, aggregation occurred only after the male occupying a tent which was probably constructed by another male. Our tagging efforts might have probably disturbed the harem but the exciting aspect of this observation is the subsequent female aggregation and the way by which a solitary male succeeded in recruiting females. In a short span of time it may not be possible for a male to succeed in mating, if it followed the primary strategy involving construction and defense of tent leading to female recruitment. In addition, we observed that the solitary male spent less time away from the roost at night after female recruitment by frequently visiting the roost throughout the night and by making several short foraging flights spaced randomly throughout the night . This behavior is consistent with the earlier reports on the activity of harem males in
Although the high clustering of females in confined roosting places appears to facilitate resource-defense polygyny in
4. Molecular genetic analysis of mating strategy
As our understanding on mating systems increases, it becomes obvious that apparently species-specific mating behaviors often vary both between and within population . Reproductive strategies are shaped by natural selection favoring individual with the greatest lifetime reproductive success. However, not all mature individuals adapt to the same reproductive strategies . When competition for access to mates is severe, young reproductive individuals sometimes opt for alternative mating behaviors. Environmental or demographic factors may constrain the number of males that were able to employ the most successful strategy . Alternative tactics in reproductive behavior enable individuals to maximize their fitness in relation to competitors of the same population. Among polygynous mammals, territorial behavior is almost exclusively a male trait believed to function primarily as a reproductive strategy to secure mates. Because mammals are committed to their progeny through gestation and lactation, female reproductive success usually is more readily quantified than male reproductive success. Male reproductive success in polygynous mammals is largely attributed to the spatial and temporal patterns of female aggregation [43, 44, 91].
Most known mating associations in bats are composed of a single male and several females and such organization are usually called harems .
4.2 Materials and methods
Bats were collected from the foliage tents of
The collected blood samples will be immediately mixed with Anticoagulant Citrate Dextrose (ACD), transferred to microcentrifuge tubes and sealed with parafilm. The blood and tissue samples will be stored in ice, transported to the lab and stored at −20°C until DNA extraction [93, 94]. No bats will be killed or retained as specimens during this project. We will be following the Institutional Ethical and Bio-safety Committee Guidelines of Madurai Kamaraj University. PCR based RAPD strategy was used to study the paternity of harem males and nearby nonharem males to the young born in the harems.
4.3 Results and discussion
During the wet (July–August) season, we captured 27 harem males, 30 nonharem males and 125 offsprings were analyzed to assign the reproductive success of harem and nonharem males. Out of the 125 offsprings the nonharem males sired 73 offsprings (average 58%) and the harem males sired only 52 offsprings (average 42%). During the dry (March–April) season 14 harem males, 18 nonharem males and 142 offsprings were captured and analyzed to assign the reproductive success of harem and nonharem males. Of the 142 offsprings the harem males sired 132 offsprings (average 94%) and the nonharem males sired only 10 offsprings (average 6%). From these results, we identified that the reproductive distribution is unequal between harem and nonharem males. It indicates that the harem males failed to control harem females thereby increasing the chances of nonharem males to fertilize some of the harem females. In addition, in southern India, during the dry season the spatial dispersion of female
The most commonly described mating system in bat species is polygyny, in which males defend a resource to recruit and have exclusive mating access with a large number of females. The resource may be a foraging area or a roosting site or the females themselves. However, several genetic analyses have shown that paternity is biased in polygynous mating systems. For e.g. a paternity study in
The molecular genetic analysis of mating strategy assignments based on RAPD results suggest that during July–August breeding season (wet), the nonharem males gained access to females and sired more offspring than March–April breeding season (dry). These results suggest that nonharem males are reproductively active, gain access to harem females and enjoy some reproductive success. To understand the reproduction of nonharem males, further investigations are necessary. Solitary behavior can be an acceptable alternative to territoriality because the reproductive success of some nonharem females were relatively high. Solitary males sired number of juveniles but had no costs for roost defense. Harem males were not able to control the movement of the females in their harems because reproduction by nonharem males is possible [2, 3, 4, 77, 93]. Since, harem females provided no parental care, the females were allowed to choose their mating partners. The behavior and reproductive success of nonharem males over their lifetime could clarify whether they potentially compensate lower reproductive success per year with longer persistence in the harem.
5. Genetic diversity within and among populations of
Genetic variation is an important factor in determining the ability of a species to adapt to new environmental conditions and therefore may be an important measure of the evolutionary potential and long-term viability of a species. The information on the amount of genetic variation within a species and its distribution within and between populations would aid in bat conservation planning [96, 97]. To understand both the past and current behavioral processes, it is vital to know the population structure of a species. Colonization and/or dispersal events can be inferred by characterization of population structure at the macro-geographical level, while social organization within a population can be used to infer the micro-geographical structure . Both direct (mark-recapture studies) and indirect (genetic) techniques  should be used to study the population structure of individuals to understand the degree of spatial variation both in distribution and genetic composition .
In general, the high dispersal abilities are associated with a low population structure , which has been reported for some mobile species, including birds  and bats . Studies describing molecular patterns of intraspecific geographical differentiation in bats have indicated a low level of genetic divergence and a limited geographical structure in species with continental distribution . However, high-intraspecific divergence levels with clearly defined geographical structuring have also been observed. These different results can be attributed to the different molecular markers used in the various studies. Studies on different bat species using the molecular genetics approach have shown genetic diversity among distant populations [102, 103, 104, 105].
5.2 Materials and methods
Extensive field trips were carried out to collect
5.3 Results and discussion
Genetic variation is the raw material of evolution and its magnitude is therefore of vital interest in governing the potential of a species to evolve and adapt . The genetic analysis of RAPD markers showed a reasonably high level of diversity. High level of polymorphism was observed in this study which indicates that the genetic base from different zonal population was diverse and extensive. The percentage of polymorphic bands of RAPD was observed to be higher in this species (73.1%). The amount of dispersal and the formation of new social groups are the two factors that strongly affect the genetic structure of the population . Population genetic data from a taxonomically diverse array of social mammals revealed low to moderately high level of genetic differentiation among social groups. This high level of heterozygosity within social groups may be a common feature of mammalian population. The majority of mammalian species exhibit a social system characterized by polygynous-mating and female philopatry .
Genetic differentiation coefficient of
Genetic studies of migratory bats support high level of gene flow among populations even when separated by large geographical distances (up to 4000 km) . Studying the migratory species using mtDNA markers can further confirm the predicted pattern with little or no genetic structure over broad distance. The individuals of lesser long-nosed bats
A greater range of genetic differentiation was identified among the migratory species. Also, a significant correlation between geographic and genetic distances is explained in several species. Extraordinarily, in the Australian ghost bat
Seasonal movement is expected to be the main influence among the populations of migratory species because the genetic structure generally appears to be low. However, a wide range of factors including dispersal ability, extrinsic barriers to gene flow and historical events determines the degree of genetic partitioning among population of sedentary species . Dispersal and migration do not essentially equate with the gene flow and hence it is important to consider this factor while accessing the impact of migratory behavior on the genetic structure of bat population. In migratory species, the level genetic structure can be low only when the individual’s mate during their migration. Patterns of genetic population structure for both migratory and non-migratory species may resemble if mating and conception in migratory species occur prior to their migration . Gene flow may also be greater than the dispersal capability of individuals of a species which might indicate, provided the population distribution is continuous. For example, radio tracking of individual brown long-eared bats
In our study, the maximum similarity was observed as many zones were closer to each other. Therefore, when populations remain closer, the gene flow is expected to be greater. As a result, the nearby populations should remain more similar at neutral loci. This relationship is referred as the method of isolation by distance and serves as the stepping stone model of gene flow . However, the distance between populations and the nature of the surrounding landscape between population are the two factors on which the level of gene flow depends . These findings support that
Our study deals with the genetic diversity in natural population of