# Phenotypic correlates between clock genes and phenology among populations of Diederik cuckoo, Chrysococcyx caprius

## TL;DR

This study explores how genetic variations in clock genes relate to timing and habitat choices in Diederik cuckoos across Africa.

## Contribution

It identifies sex-specific phenotypic correlations between clock gene alleles and phenology in a migratory bird species.

## Key findings

- Shorter alleles in Adcyap1 correlate with habitat selection, while longer alleles in Clock correlate with timing.
- Clock alleles with 10 polyglutamine repeats are more frequent and homozygous in northern populations.
- Genetic diversity in circadian genes may influence adaptation to environmental changes like climate and urbanization.

## Abstract

The Diederik cuckoo, Chrysococcyx caprius, is a small Afrotropical bird in the family Cuculidae. It is taxonomically related to 13 other species within the genus Chrysococcyx and is migratory in sub‐Saharan Africa. It has a unique breeding behaviour of being a brood parasite: Breeding pairs lay their eggs in the nests of a host species and hatchlings expel the eggs of the host species. The aim of the present study was to investigate diversity in two circadian clock genes, Clock and Adcyap1, to probe for a relationship between genetic polymorphisms and their role in circannual timing and habitat selection (phenology) in intra‐African migrants. DNA extracted from blood was used for the PCR amplification and sequencing of clock genes in 30 Diederik cuckoos. Three alleles were detected for Clock with similar genotypes between individuals from the Northern and Southern breeding ranges while 10 alleles were detected for Adcyap1, having shorter alleles in the North and longer alleles in the South. Population genetic analyses, including allele frequency and zygosity analysis, showed distinctly higher frequencies for the most abundant Clock allele, containing 10 polyglutamine repeats, as well as a high degree of homozygosity. In contrast, all individuals were heterozygous for Adcyap1 and alleles from both regions showed distinct differences in abundance. Comparisons between both clock genes and phenology found several phenotypic correlations. This included evidence of a relationship between the shorter alleles and habitat selection as well as a relationship between longer alleles and timing. In both instances, evidence is provided that these effects may be sex‐specific. Given that these genes drive some of the synchronicity between environments and the life cycles of birds, they provide valuable insight into the fitness of species facing global challenges including climate change, urbanisation and expanding agricultural practices.

The Diederik cuckoo is a small Afrotropical bird in the Cuculidae family that has a wide geographic distribution in sub‐Saharan Africa. A study on 30 Diederik cuckoos revealed genetic diversity in Clock and Adcyap1 circadian clock genes, with distinct North–South variations in allele lengths. Phenotypic correlations indicated relationships between allele lengths, habitat selection and timing, in a potentially sex‐specific manner, offering valuable insights into the species' adaptation to global challenges.