Cryptic sexual dimorphism reveals differing selection pressures on continental islands

• Published in: Biotropica Vol. 53; no. 1; pp. 121 - 129
• Main Authors: Ó Marcaigh, Fionn, Kelly, David J., Analuddin, Kangkuso, Karya, Adi, Lawless, Naomi, Marples, Nicola M.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.01.2021
• Subjects: babblers; Biomedical materials; Breeding; Clustering; Dan protein; density‐dependent evolution; Ecological distribution; Ecological niches; Genetic analysis; Geological history; Indonesia; intersexual competition; Islands; Morphology; Morphometry; Niche overlap; Niches; Pellorneidae; Pellorneum; Sexing; Sexual dimorphism; size dimorphism; Species; Sulawesi; Wallacea; Wallacea; Sulawesi; Indonesia
• ISSN: 0006-3606; 1744-7429
• DOI: 10.1111/btp.12852

Birds are well known for their sexual dimorphism. But not all forms of dimorphism are the same, and differences in morphology can be so subtle that they are not detected by casual observation. We report that this is the case with the Sulawesi Babbler (Pellorneum celebense), the first reported instance of sexual dimorphism in this species or any of the ground babblers of the South‐East Asian islands. Our finding is based on a combination of morphometric analyses, genetic sexing, and observation of breeding condition. We highlight the utility of unsupervised clustering approaches, widely used in the biomedical literature, for the investigation of sexual dimorphism in ecological and evolutionary contexts. The sexual dimorphism was weaker on the mainland of Sulawesi and stronger on the continental islands of Kabaena, Muna, and Buton. This suggests that different evolutionary pressures have led the species to partition niches differently in these habitats, which separated only recently in geological history. This kind of intraspecific niche partitioning is an intrinsic part of the ecological niche of such species, one we must not miss if we are to fully understand these endlessly fascinating organisms and systems. in Bahasa Indonesian is available with online material Abstrak Burung terkenal karena dimorfisme seksualnya. Namun tidak semua bentuk‐bentuk dimorfisme burung adalah sama, dan perbedaan‐perbedaan dalam hal morfologi sangat halus sehingga mereka tidak terdeteksi oleh pengamatan biasa. Kami melaporkan hal ini pada Pelanduk Sulawesi (Pellorneum celebense), contoh pertama dimorfisme seksual yang telah dilaporkan untuk spesies ini atau spesies pengoceh tanah manapun di pulau‐pulau Asia Tenggara. Temuan kami didasarkan pada kombinasi dari analisis morfometrik, jenis kelamin genetik, dan pengamatan pada kondisi penangkaran. Kami menjelaskan kegunaan pendekatan pengelompokan yang telah banyak digunakan dalam literatur biomedis, untuk investigasi dimorfisme seksual dalam konteks ekologis dan evolusi. Dimorfisme seksual terlihat lebih lemah di daratan Sulawesi dan lebih kuat di pulau‐pulau benua dari Kabaena, Muna, dan Buton. Hal ini menunjukkan bahwa tekanan evolusi yang berbeda telah menyebabkan spesies memisah‐misahkan relung berbeda di habitatnya, yang belum lama terpisahkan secara geologis. Pemisahan relung intraspesifik semacam ini adalah bagian intrinsik dari relung ekologis spesies tersebut, yang tidak boleh kita abaikan jika kita ingin memahami sepenuhnya organisme dan sistem‐sistemnya yang menarik sampai kapanpun. We found two morphological clusters in the population of the Sulawesi Babbler, a shy brown bird previously thought sexually monomorphic. Genetic sexing work showed the larger birds had ZZ chromosomes (male) and the smaller ZW (female). This dimorphism has grown to be more pronounced on the continental islands of Kabaena, Muna, and Buton, even though they've been isolated for only a brief period.