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|Title: ||Effects of experience on the development of social behaviour of house-dwelling bats|
|Other Titles: ||Effetti dell'esperienza sullo sviluppo del comportamento sociale nei chirotteri antropofili|
|Authors: ||ANCILLOTTO, LEONARDO|
|Tutor: ||Boitani, Luigi|
|Issue Date: ||7-Nov-2014|
|Abstract: ||This study aims at clarifying the mechanisms underlying the formation and maintenance of
stable social units in bats (Chiroptera), a characteristic shared by most species of this group of
mammals, by investigating the effects of the early social environment, i.e. pursuing the
hypothesis that imprinting-like influences on the development of social behaviour exist and
may have a profound impact on the social lives of bats.
First I present an overview on bats' social behaviour and systems: these mammals comprise a
high number of species and thus constitute an excellent group for testing general hypotheses
about evolution and development of social behaviour. Bat social systems in fact range from
solitary species to others aggregating in conspicuous groups of up to millions individuals.
Such complexity leads to a variety of social behaviours rarely found in other taxonomic
groups: there is increasing evidence that bats are able of cooperative social behaviours such as
allogrooming, communal nursing, group hunting and social learning, all interactions that
require high-level cognitive skills.
Investigating such a complex system needs a multi-disciplinary approach, fundamental for
disentangling the mechanisms through which bat sociality develops. I performed a series of
experiments and used classical ethological and statistical methods (ethogram composition,
general linear models) together with social network analysis (SNA), developing the analyses
of social interactions on an individual-based approach.
Experiment 1 deals with the ability of bats to modulate their behaviour (e.g. aggressiveness)
according to intrinsic (e.g. age, sex) and extrinsic (familiarity) factors during a social
interaction. I performed dyadic arena-encounters where two bats per test were allowed to
freely interact. I recorded aggressive and affiliative behaviours and measured the degree of
affiliation towards familiar and unfamiliar individuals of captive European free-tailed bats
(Tadarida teniotis). By testing individuals from different captive colonies and of different
age, I measured the effects of familiarity, sex and age on the aggressive behaviour of this
species, using aggressiveness as a proxy for xenophobia. I found significant effects of all the
selected factors upon the degree of affiliation among individuals: familiar bats were more
prone to perform affiliative behaviours, behaving xenophobically towards non-group
members. This xenophobic attitude was lower in females and almost null towards juveniles.
These results indicate that adult bats' behaviour is influenced by previous social experiences,
also suggesting that social bonds formed inside colonies are long lasting regardless of genetic
relatedness existing between individuals.
With experiment 2 I investigate the mechanisms leading to the formation of social subunits in
groups bats, using Pipistrellus kuhlii as a model species. By manipulating the early social
environment of young bats and describing their pattern of association inside artificial roost as
well as measuring their rates of interaction, I demonstrate that spatial proximity inside roosts
promotes social cohesion. These associations are maintained by bats throughout adulthood by
means of cooperative behaviours such as allogrooming and social thermoregulation. Both
classical approach and social network analysis of interacting bats indicate that physical
contacts and cooperative behaviours among bats inside a colony are non-random and are more
frequently performed between individuals that already had contacts at a very young age.
Following the same approach and techniques of Experiment 2, with Experiment 3 I test the
hypothesis that the same mechanisms that produce group cohesion inside roosts can lead to
the formation of multi-specific associations of bats. Such multi-specific groups are
widespread among mammals, and in bats they are assumed to form due to eco-physiological
reasons (i.e. species sharing micro-climatic requirements). I manipulated the early social
environment of two species that naturally occur inside the same roosts; very young Kuhl's (P.
kuhlii) and Savi's (Hypsugo savii) bats were exposed to artificial multi-specific social contacts
in captivity. I demonstrate that early social experience does influence social bonding also
beyond the species' boundaries. Independent young bats in fact selected previous groupmembers
for social thermoregulation and reciprocal grooming, regardless of species
Results from all experiment clearly indicate a strong effect of early social environment on the
interaction and association patterns in bats, both at short (Experiments 2-3) and long
(Experiment 1) time scales, suggesting the existence of imprinting-like mechanisms. Such
mechanisms lead to the formation of cryptic social subunits within bat colonies and probably
enhance the cohesion of the entire social structure, with obvious and strong consequences on
behavioural and ecological (e.g. demographic and epidemiological) scales.|
|Appears in PhD:||BIOLOGIA ANIMALE|
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|Tesi_Finale_LeonardoAncillotto.pdf||Articolo principale||2.92 MB||Adobe PDF|
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