Speciation by host switch in brood parasitic indigobirds

Area of Science:

• Evolutionary Biology
• Ornithology
• Speciation Research

Background:

• Sympatric speciation, where new species arise from a single ancestral species occupying the same geographic region, is theoretically plausible but empirically challenging to demonstrate.
• African indigobirds (Vidua spp.) are brood parasites known for their host-specific behaviors, including mimicry of host young's mouth markings and adult host songs.
• These mimicry behaviors are crucial for mate choice and nest parasitism, potentially driving reproductive isolation within indigobird populations.

Purpose of the Study:

• To investigate the genetic differentiation among African indigobird species.
• To test the hypothesis that host-specific imprinting in both sexes contributes to recent sympatric speciation in indigobirds.
• To compare the speciation mechanisms in indigobirds with those in other brood parasites like the common cuckoo.

Main Methods:

• Genetic analysis comparing mitochondrial haplotype and nuclear allele frequencies across different indigobird species.
• Behavioral observations focusing on host-specific mimicry in nestlings and adults (song and mouth markings).
• Comparative analysis with known speciation mechanisms in related brood parasitic species.

Main Results:

• Indigobird species are genetically similar overall, but show significant differentiation in mitochondrial and nuclear genetic markers.
• Strong evidence supports recent sympatric speciation, driven by host-specific imprinting in both male and female indigobirds.
• Unlike the common cuckoo, where only females show host fidelity, both sexes in indigobirds imprint on hosts, facilitating speciation.

Conclusions:

• The genetic and behavioral data strongly support a model of recent sympatric speciation in African indigobirds.
• Host-specific imprinting by both male and female indigobirds is a key mechanism driving reproductive isolation and the formation of new species.
• Indigobirds offer a well-understood empirical example of sympatric speciation, highlighting the role of behavioral imprinting in evolutionary divergence.