 THE SAC-WINGED BAT PROJECT
Christian C. Voigt and Barbara Caspers
1. Reproductive strategies of males
2. Chemical
signals
3.
The social regulation of harem take-overs
4.
Reproductive biology and endocrinology
The sac-winged bat (Fig.1), Saccopteryx bilineata, has
a broad distribution range from Mexico to south-eastern Brazil.
Colonies of this insectivorous bat include up to 50 individuals.
Sac-winged bats roost in well-lit buttress cavities, in the cavities
of old trees, but can also be found around old buildings. Our main
study colony is located in the Caribbean lowland rainforest at the
biological station "La
Selva" of the "Organisation for Tropical Studies"
in Costa Rica.
1. Reproductive strategies of males
The mating system of Saccopteryx bilineata has been
described as harem-polygynous, because males defend territories
with up to nine females. Peripheral males roost in proximity of
such harems and interact frequently with the harem holder and also
with the females. In a joined project with Dr. Frieder Mayer (University
of Erlangen-Nürnberg) we are studying the male reproductive
success and what male traits define the reproductive success. On
average, harem males father only 30% of the offspring within their
harem. The majority of offspring is fathered by other harem males,
peripheral males or by males from outside the colony. However, harem
males sire on average more offspring than peripheral males. Therefore,
males benefit in terms of sired offspring from harem ownership.
2. Chemical signals
In contrast to the female Saccopteryx bilineata, males
possess a sac-like organ (Fig. 2) with numerous infoldings in their
front wing membrane. The wing sacs contain a brownish, sweet-smelling
liquid, which is used in several contexts, e.g. the hovering flight
(Fig. 9). Especially after dawn and before dusk, when the activity
in the colony is highest, males hover in front of females. While
hovering the wing sacs are snapped open and males fan their perfume
towards the roosting female. Hovering flights can last up to 14
s. Further observations demonstrate that the wing sacs are also
open when a male is approaching a female (so called "salting"
Fig. 3) and also during copulation.
The wing sacs lack any glands. Observations at the roosting site
showed that male sac-winged bats mix their perfume (Fig. 7) every
afternoon during a time-consuming stereotype behaviour. When blending
their perfume males first clean their wing sacs and then fill it
with several secretions like saliva, urine and secretion from various
glands.
In cooperation with Dr. Frank C. Schroeder and Prof. Dr. Jerrold
Meinwald (Cornell University) as well as Dr. Stephan Franke (University
of Hamburg), we investigate the male specific substances to find
out whether they act as sexual pheromones e.g. for female attraction.
Furthermore we analyse individual odour profiles to investigate
whether individual, colony- or age-specific or seasonal differences
exist among the male odour profiles. In an additional cooperation
with Dr. Stephanie Speck (IZW) and PD Dr. Martin Dehnhard (IZW)
we investigate the influence of bacterial metabolism on the production
of odour. The main aim of this study is to understand the role of
odour in mate choice decision of Saccopteryx bilineata.
3. The social regulation of harem take-overs
By removing males temporarily from their harem territory, we
tested which traits predispose non-harem males to take over a harem.
Our experiments showed that non-harem males form peripheral groups
with a hierarchical structure according to the length of time males
are present in the colony, i.e. males of the peripheral groups that
are present for the longest time in the colony are the follow-up
males of the corresponding harem males. The necessity to establish
familiarity with territories and possibly also with females as early
as possible in a male’s life, may lead to the phenomenon of male
philopatry in this mating system.
4. Reproductive biology and endocrinology
Female sac-winged bats give birth to a single offspring per year.
The mating season is restricted to a short time period half a year
prior to parturition. In collaboration with Prof. Dr. Franz Schwarzenberger
(Veterinärmedizinische Universität Wien) and PD Dr. Martin Dehnhard
(IZW) we are studying the metabolites of sexual hormones in the
faeces of sac-winged bats with respect to the general endocrinology
of reproduction and the influence of social status and dominance
on reproduction in this species
1. male sac-winged bat; 2. wing sac of a male sac-winged bat
3. "salting" of a male sac-winged bat, wing sac is open;
4. equipment for collecting wing sac secretion; 5. catching sac
winged bats 6. glas vials with a cotton ball to wipe out the wing
sac; 7. chromatogramm of an odour sample; 8. roosting site of a
study colony in Costa Rica; 9. male while hovering in front of a
female 10. retangling a sac winged bat out of the mist net.
NICHE PLASTICITY IN NEOTROPICAL BATS
Katja Rex, Dr. Christian Voigt
(DFG financed)
In the project „niche plasticity in Neotropical bats“ we are
studying the mechanisms that promote the coexistence of species
in the assemblages of leaf-nosed bats. The family of leaf-nosed
bats (Phyllostomidae) is the second largest within the order of
bats, even though it is endemic only to the Neotropics. Many assemblages
of this family exhibit an extremely high species richness compared
to other families of mammals. So far we know little about the mechanisms
that sustain such a high species richness, e.g. niche partitioning
among members of the assemblage. This project aims to investigate,
if leaf-nosed bats adjust their dietary niches to a different species
richness of the assemblage. Three bat assemblages with different
species richness will be compared to see if
a) the dietary niches of species
in an assemblage with high species richness overlap more than in
an assemblage with fewer species, and
b) if species that occur at
more than one study site adapt their dietary niche to the changes
in species composition of the assemblage.
Vampyrodes
carracioli Bat in cotton
bag Chrotopterus
auritus
Study sites
 Biological
research station La Selva (LS), Costa Rica:
This study site is located in the Caribbean lowland rain forest
of Costa Rica about 10° Northern latitude. The bat assemblage of
LS has been studied intensely for the last 20 years. 72 bat species
have been recorded at this site, 48 of them are leaf-nosed bats.
Tiputini Biodiversity Station
(TBS), Ecuador:
TBS is located in the Amazonian rain forest of Ecuador, almost
at the equator, and is known as one of the most divers areas of
the planet. According to our data about 100 bat species share this
habitat, 70 of which are leaf-nosed bats. The full bat inventory
of TBS is not yet known, our investigations are still in progress.
Podocarpus
National Park (PNP), Ecuador:
Podocarpus National Park is located in the Andean mountains of
Southern Ecuador at an altitude of about 1000m above sea level.
Our study site includes a section of the park near the Rio Bombuscaro.
According to our calculations about 50 species of bats coexist here,
30 of which are leaf-nosed bats.
Morphology and stable isotopes
The dietary niche of each bat species will be described by several
parameters. Morphological parameters such as body size, body mass,
wing dimensions and wing loading will be measured. The analysis
of the stable isotope composition in small samples o bat wing tissue
allows to determine the trophic position and spatial distribution
of the species.
Measuring
wing morphology
Publications:
Rex K, Kelm D, Wiesner K, Matt F, Kunz TH, Voigt CC (in prep).
How many species can coexist in Neotropical rainforest? Species
richness and structure of phyllostomid bat assemblages
Feeding ecology and metabolic physiology of plant-feeding bats
Detlev H. Kelm, Christian C. Voigt
Diet, besides body mass, is assumed
to markedly influence the metabolic rate of animals. However, the functional
link between diet and metabolism remains unclear.
Within mammals, neotropical
leaf-nosed bats (Phyllostomidae) are an ideal model group for investigating the
connection between diet and metabolic rate. This family includes more than 100
closely related species that exhibit a variety of different feeding habits,
including carnivory, insectivory, phytophagy, piscivory and even blood-feeding.
We conduct behavioural experiments
in the field, feeding trials and laboratory measurements, in order to quantify
the effect of diet on the activity- and energy budgets and digestive physiology
of phytophagous bats. We are especially interested in the question of how
foraging strategies and metabolic rates are related. Our studies mainly focus
on the species Glossophaga commissarisi,
which feeds seasonally on nectar and fruits (Fig. 1 and 2).
 
Fig. 1: Glossophaga
commissarisi feeling at a Piper
auritum. Fig. 2: Glossophaga commissarisi ingesting
nectar at a Werauhia gladioliflora flower.
Funded by the
Deutsche Forschungsgemeinschaft (Vo 890/10)
The role of odours for mate choice and social structure in Noctilio
albiventris, the lesser Bulldog bat
Dina Dechmann, Christian C. Voigt
 Although
odours are essential for communication among group living mammals
and for mate choice, they remain poorly understood. In our Noctilio
project, we investigate the mechanisms of group living and the role
of chemical signals for social foraging, using a particularly interesting
bat species as a model. Noctilio albiventris - the lesser bulldog
bat - has two external scent organs, both of which do not contain
scent-producing glands: the subaxial patch and the sexually dimporphic
inguinal pockets. The subaxial patch is probably formed when the
females, who live in small stable groups rub their faces under each
others arms, depositing the secretions of their facial glands there.
By mixing their individual odours a group odour is created, which
may help to distinguish foreign animals when they enter a roost
and prevent them from joining the group during social foraging.
In contrast, the function of the inguinal pocket of the male
is probably to produce cues for mate choice and thus it should be
subject to sexual selection. We investigate the mechanisms of social
foraging and the evolution of the two scent organs using various
methods such as automated telemetry, molecular analyses of relatedness
and paternity, as well as bacteriological and chemical analyses.
The project is a multidisciplinary cooperation between behavioural
ecologists,
microbiologists, geneticists and chemical ecologists,
most of them colleages at the IZW.
The aim of the project is to understand the role of bacteria
in the creation of socially relevant odours, to deepen our understanding
of sociality in mammals, and to corroborate the essential role of
odours for intra and intersexual communication.
|
