Sex determination in Turdus amaurochalinus (Passeriformes: Muscicapidae): morphometrical analysis supported by CHD gene

Abstract

Sex determination is important for conservation and population studies, particularly for reproduction programs of threatened species and behavioural ecology. Turdus amaurochalinus, Creamy-bellied Thrush, only exhibits sexual dimorphism during the breeding season, when males are considered to show intense yellow bills, and females and immature males show dark brown bills. The objectives of this study were: 1) to determine the sex of individuals using genetic techniques, and 2) to test the hypothesis that sex dimorphism can be detected by morphometry. This study was carried out at Parque Nacional da Restinga de Jurubatiba, a preserved area located on the North coast of Rio de Janeiro State. The birds were captured using ornithological nets, singly marked with metal rings, weighed, measured and had blood samples collected before being released. The sex of 42 T. amaurochalinus individuals was determined using the CHD gene marker. A total of 20 males and 22 females were identified from June to August, with peak capture frequency in June. Turdus amaurochalinus females and males differed significantly in morphometrical measures. The most important traits to distinguish males from females were wing length (Student t-test=4.34, df=40, p=0.0001) and weight (Student t-test=2.08, df=40, p=0.044): females were heavier and had significantly shorter wing length than males. Females and males were correctly classified in 86% and 75% of cases, respectively, using Discriminant Analysis. The molecular analysis was the most secure method for sex determination in the studied species. Rev. Biol. Trop. 59 (2): 789-794. Epub 2011 June 01.

Potential of Inter- and Intra-Species Variability of CHD1 Gene in Birds as a Forensic Tool

“…When it comes to sex determination in sampled birds using a dye-labelled CHD1F/CHD1R primer set, capillary electrophoresis proved to be an accurate, fast, and reliable method. Our results confi rmed that the specifi ed method enabled accurate sex determination in all tested species, although end point PCR approach was also highly successful, as shown here, but also in previous studies [7,9,10,26,27].…”

Estimation of Adult Sex Ratio and Size-Related Sexual Dimorphism Based on Molecular Sex Determination in the Vulnerable La Selle Thrush, Turdus swalesi

“…Radio-tracking of individuals of both sexes (see Aubry et al, [ 75 ]) might be useful in the future to document seasonal variation in movements and home ranges of the species. Third, a higher proportion of males than females has been previously reported in several tropical Turdus species [ 11 , 46 , 64 , 76 ]. The overall male-biased adult sex ratio observed in the present study could thus be a particular feature of the Turdus species in tropical forests if, for instance, adult survival rate tends to differ between the two sexes [ 70 , 77 ].…”

“…Previous studies on other turdid species relied exclusively on blood samples to obtain DNA for molecular sexing [ 11 , 46 , 47 , 63 , 64 , 65 ]. Here, we used both blood and contour feathers with equal success to assign a sex to individuals.…”

“…However, we evidenced a subtle, albeit significant, sexual dimorphism in body size in the La Selle Thrush, with median tail length being about 10% longer in males compared to females, and median wing length being about 3.5% longer, with both characters being positively correlated between themselves. Similarly, several studies found that wing length was sexually dimorphic and longer in males of thrush species [ 11 , 46 , 47 , 63 , 64 , 65 , 79 ], whereas tail length was seldom included in the analysis of sexual dimorphism in turdid species (however, see Frey et al [ 79 ]). Although direct evidence is lacking for the La Selle Thrush, wing flicking and tail raising have been observed during ritualized aggressive encounters in other thrush species [ 80 , 81 ], such that the observed sexual dimorphism may indicate potential male social dominance over females.…”