BEHAVIOURAL ECOLOGY
Isabelle Amat Æ Marcela Castelo
Emmanuel Desouhant Æ Carlos Bernstein
The influence of temperature and host availability on the host exploitation
strategies of sexual and asexual parasitic wasps of the same species
Received: 26 January 2005 / Accepted: 2 December 2005 / Published online: 19 January 2006
Ó Springer-Verlag 2006
Abstract In the hymenopteran parasitoid Venturia
canescens, asexual (obligate thelytoky not induced by
Wolbachia bacteria) and sexual (arrhenotokous) wasps
coexist in field conditions despite the demographic cost
incurred due to the production of males by sexual fe-
males. Arrhenotoky predominates in field conditions,
whereas populations in indoor conditions (mills, gra-
naries) are exclusively thelytokous. These differences in
the relative abundance of the two modes of reproduction
between environments suggest that the individuals of
each reproductive mode may have developed strategies
adapted to the conditions prevailing in each kind of
habitat. The two environments contrast in temperature
variability and in the spatial heterogeneity of host
availability. In this study, we considered the combined
effect of temperature and host availability on host patch
exploitation by thelytokous and arrhenotokous V.
canescens. As expected, arrhenotokous females were
more sensitive to temperature changes. If the tempera-
ture decreased before foraging, they remained longer
and exploited patches more thoroughly. This is consis-
tent with the expected behaviour of parasitoids in re-
sponse to signs of unfavourable conditions that entail
increasing risk of time limitation or a reduced proba-
bility of attaining further patches. Both arrhenotokous
and thelytokous females increased patch exploitation
with host availability. However, unexpectedly, we found
no difference in the way the two types of wasp responded
to differences in host availability. Differences in the
strategies adopted under different environmental con-
ditions may indicate divergence of niche-specific life
history traits between the two modes of reproduction.
Niche displacement may partly account for the coexis-
tence of these two modes of reproduction at a geo-
graphical scale.
Keywords Reproduction modes’ coexistence Æ
Habitat specialisation Æ Patch-leaving decision Æ
Proportional hazards model Æ Venturia canescens
Introduction
According to demographic considerations, sexual
reproduction entails a competitive disadvantage when
compared with asexual reproduction, due to the cost of
producing males (Maynard Smith 1978). The predomi-
nance of sexual reproduction in nature therefore seems
paradoxical. Two possible explanations for the success
of sexual reproduction based on long-term processes
have been proposed: sex accelerates the rate of evolu-
tionary change (Mu
¨
ller 1932; Crow and Kimura 1965)
and, by recombination, prevents the accumulation of
deleterious mutations (Mu
¨
ller 1964; Haccou and
Schneider 2004). However, arguments based on long-
term processes cannot account for the coexistence of
sexual individuals and asexually reproducing competi-
tors observed in some systems. These conditions call for
explanations based on short-term processes of how
sexual individuals compensate for the immediate cost of
producing males (Williams 1975).
The relative fitness of sexual and asexual animals may
depend on environmental conditions, so ecological
mechanisms may account for the short-term advantages
of sex (Hamilton 1980; Bell 1982; Case and Taper 1986;
Communicated by Roland Brandl
I. Amat (&) Æ E. Desouhant Æ C. Bernstein
Laboratoire de Biome
´
trie et Biologie Evolutive (UMR 5558),
CNRS, Universite
´
Lyon 1, 43 boulevard 11 novembre,
69622 Villeubanne Cedex, France
E-mail: amat@biomserv.univ-lyon1.fr
Tel.: +33-4-72432929
Fax: +33-4-72431388
M. Castelo
CONICET, Laboratorio de Ecologı
´
a y Comportamiento Animal,
Dpto. de Ecologı
´
a, Gene
´
tica y Evolucio
´
n, Facultad de Ciencias
Exactas y Naturales, Universidad de Buenos Aires,
Ciudad Universitaria, Pabello
´
n II,
C1428EHA Ciudad de Buenos Aires, Argentina
Oecologia (2006) 148: 153–161
DOI 10.1007/s00442-005-0332-9