no-choice experiments female-choice experiments

Margarida Bárbaro, Mário Mira, Inês Fragata, Pedro Simões, Margarida Lima, Miguel Lopes-Cunha, Bárbara Kellen, Josiane Santos,
Margarida Matos and Sara Magalhães
Faculdade de Ciências da Universidade de Lisboa, Centro de Biologia Ambiental, Departamento de Biologia Animal, Lisboa, Portugal
When a population invades an environment already occupied by conspecifics, the fate of the introgression depends on both differences in relative fitness and
reproductive isolation. Here we present a study on the evolution of reproductive barriers of Drosophila subobscura populations, after being introduced to a
common laboratorial environment. Will females exhibit a sexual preference for males of their own population? If so, will this preference change during
adaptation to the laboratory?
Drosophila subobscura individuals were
GRO1
collected from the two extremes of the
GRO2
GRO3
European latitudinal cline. Populations
AD1
AD2
AD3
were three-fold replicated at generation
4 and maintained at 18°C with controlled
densities and 12L:12D. Assays of mating
behaviour (no-choice and female-choice)
were conducted at generations 5, 10 and 17. The traits analyzed for no-choice experiments
were frequency of matings (FM), Courtship Latency (CL) and Courtship Duration (CD). As for
female-choice experiments, the Isolation Index (I.I.) was estimated which is the ratio of the
difference between the frequencies of homogamic and heterogamic matings to the sum of the
two. The I.I. is 1 if sexual isolation is complete, 0 if matings are random and negative if
Although there were significant differences across generations in the variable CD
heterogamic matings outnumber the homogamic ones.
(ANCOVA, P<0.05), no trend was observed. At generations 5 and 10, no differences
were found between females or males (ANOVA, P>0.05). And at generation 17,
NO-CHOICE EXPERIMENTS
courtships to Ad females were longer than courtships to Gro females (ANOVA,
P<0.05).
FEMALE-CHOICE EXPERIMENTS
Gro individuals preferred to mate with individuals of the same population (homogamic
matings) more than Ad individuals (t-test, P<0.05) at generations 5 and 17, but not at
generation 10. Overall, the Isolation Index decreased along generations, but not
significantly (Log-linear Analysis of Frequencies, P>0.05).
There was a significant increase of FM across generations (ANCOVA, P<0.05). At
generation 5 Gro females mated more than Ad females (ANOVA, P<0.05), however
there were no differences between males (ANOVA, P>0.05). As for generations 10 and
17, no differences were found between the performances of both males and females
(ANOVA, P>0.05).
At generations 5 and 17 Gro males mated more than Ad individuals (Log-linear Analysis
of Frequencies, P<0.05). Comparing generations 5 and 10, Ad males mated more at
generation 10 than at generation 5 (Log-linear Analysis of Frequencies, P<0.05). Gro
error bars correspond to
the standard errors of
the three replicates of
each population
males increased their number of matings compared to Ad males between generations
Overall there was an increase in the number of matings across generations
10 and 17 (Log-linear Analysis of Frequencies, P<0.05). Also, there were significantly
(Log-linear, P<0.05). But there were no significant differences across
more matings at generation 17 than at generation 10 males (Log-linear, P<0.05). Overall
generations in the isolation index.
there was an increase in the number of matings across generations (Log-linear Analysis
of Frequencies, P<0.05).
CL significantly decreased across generations (ANCOVA, P<0.05). At generation 5 Gro
• GRO POPULATIONS IN GENERAL WITH BETTER PERFORMANCE THAN
AD POPULATIONS
males initiated courtship sooner than Ad males (ANOVA, P<0.05). As for generation 10
• MATING PERFORMANCE INCREASED OVER TIME
no differences were observed between females or males (ANOVA, P>0.05). And at
• ASYMMETRY IN REPRODUCTIVE ISOLATION OBSERVED
generation 17 Gro males started courting sooner than Ad males (ANOVA, P<0.05) and
• DISASSORTATIVE MATING OF THE SOUTHERN POPULATIONS FADED
Gro females were courted sooner than Ad females (ANOVA, P<0.05).
AWAY DURING LABORATORY EVOLUTION
Acknowledgments
This study was partially financed by “Fundação para a Ciência e Tecnologia” (FCT) project nº PTDC/BIA-BEC/098213/2008. M. Mira had a grant from Fundação Amadeu Dias, I.F. has a PhD grant (SFRH/BD/60734/2009), P.S. has a Post-Doc grant
and M.C. has a BI grant from FCT. J.S. had a PhD grant (SFRH/BD/28498/2006) and B. K. and M. L. had BTI grants from FCT.