Download Song divergence in response to recent anthropogenic habitat

Song divergence in response to recent anthropogenic habitat changes in an oceanic island
(São Tomé, Africa) endemic passerine (Speirops lugubris)
Andrea Baquero¹* , Martim Melo², Claire Doutrelant²
[1] Laboratorio de Biología Evolutiva de Vertebrados, Universidad de los Andes, Bogota, Colombia
[2] Centre d’EcologieFonc5onnelle et Evolu5ve/ CNRS Montpellier, France *Email: [email protected]
INTRODUCTION
METHODS
The impact of human activities on natural ecosystems is ubiquitous. The changes in
direction and strength of natural and sexual selection that arise in human altered
environments due to changes in ecological factors might promote divergence among
populations even if these are not isolated, provided selection is sufficiently strong. In
birds, such novel selective pressures may lead to divergence in phenotypic traits affecting
both ecological adaptation and mate recognition.
Song recordings were collected from individuals on both primary
forest and plantation sites which differ in vegetation composition and
structure. Song structure was analyzed with Raven Pro sound analysis
software, measuring temporal and frequency characteristics from 40
individuals from forests and 39 from plantation sites.
In this study, we assess the divergence of song as a mate recognition trait in response to
habitat differentiation caused by human alteration of the environment in the São Tomé
Speirops (Speirops lugubris), a passerine bird endemic to this oceanic island in the Gulf of
Guinea, Africa. We compare song structure between individuals occurring in primary
forest and in shaded plantations established c. 1t0 years ago, in order to determine if
microevolutionary changes can take place over such a small spatial and temporal scale,
and in the presence of gene flow.
Results of this study are relevant in understanding the evolutionary responses of small
island populations to human‐altered environments.
Gulf of Guinea Island System, São Tomé Island. Sampling locations. Forest sites in
green, Plantations sites in red. Map adapted from Jones and Tye (2006)
RESULTS AND DISCUSSION
The S.lugubris song varied between habitat types in temporal (notes
per song, pace) and frequency structure (peak frequency) patterns.
Forests are closed habitats with numerous sound barriers that limit
temporal patterning due to reverberations occurring with high paced
songs. Frequency structure is also restricted because of barriers
imposing sound attenuation, where high frequencies are easily lost
with obstacles. Birds from forests were found to sing slower paced
and lower frequency songs than those from plantations. These
results follow in the direction predicted by the sound environment,
suggesting a strong influence of the differential habitat structure.
Discriminant function scores for Forest (green) and Plantation (Orange) habitats.
Function 1: Peak Frequency, Number of Notes, and Pace (9ti.6% of variation).
Function 2: Length of song, Low Frequency, Delta Frequency (4.4% of variation).
Group centroids are represented by black symbols. λ‐W: 0.titi7, DF: 14, P= 0.014*
This was also found for morphological characteristics in S.lugubris which vary between habitat types (A. Baquero
unpublished data). Birds in Forests are significantly larger than those in Plantations, suggesting a strong
environmental influence on morphological variation. Though no direct correlation could be tested between
morphological measurements and song features, the occurrence of lower frequency songs and slower singing pace in
forests environments where birds exhibit larger bills and greater body mass, is also consistent with the hypothesis
that differences in song features may arise as a result of morphological adaptation.
Plumage coloration analysis was also conducted finding no significant differences between forest and plantation
birds. Theory suggests that sexual selection favours traits that are most conspicuous, less costly or are a more
accurate signal of the individual’s fitness condition in a particular environment. Thus, if there is a constraint on sexual
chromatism, alternative traits such as song may replace chromatism as the trait under sexual selection. This could be
possible in Speirops lugubris because its song is very elaborate and complex, and as we show here, it was found to
diverge according to habitat types.
Means and standard deviations for song variables for forest
and plantation. N:79 individuals, Forests N:40, Plantations N:39.
ANOVA ****P<0.0001, ***P<0.001, **P<0.005, *P<0.01
CONCLUSION
These results suggest that the endemic Speirops lugubris is experiencing an adaptive and potentially evolutionary
response to diverging habitat structures caused by anthropogenic destruction of the original environment.
Furthermore, this study supports the hypothesis that ecological adaptation to human modified habitats may
drive signal evolution even in the face of gene flow.
ACKNOWLEDGMENTS
REFERENCES
Special thanks go to C.D. Cadena for his support, numerous corrections
and guidance. For their assistance, we thank the Centre d’Ecologie
Fonctionnelle et Evolutive (CRNS, France), the Laboratorio de Biología
Evolutiva de Vertebrados (Universidad de los Andes, Colombia), the field
guides of the Associaçao Monte Pico and the community in São Tomé.
Financial support for this project was provided by the Rufford Small
Grants Foundation and the British Ecological Society. The AOU/COS/SCO
student travel grant allowed us to attend this meeting.
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S.lugubris (A.Baquero)
Primary Forest (A.Baquero)
Primary Forest (M.Melo)
Coffee Plantation (A.Baquero)
S.lugubr
is