Testis Size and Asymmetry in the Guinea Fowl (Numida Meleagris): A Test of the Compensation Hypothesis

Abstract

Despite numerous studies on testicular asymmetry in birds, there are still inconsistent reports on the pattern of asymmetry in species belonging to various phylogenetic groups and exhibiting diverse lifestyles. In addition, there is a lack of clarity on whether functional differences exist between the left and right testes despite differences in size, as well as no evidence of naturally occurring compensation in testis size in terrestrial and galliform birds. A study involving 400 Guinea Fowl (Numida meleagris) cocks was conducted to determine asymmetry and compensatory growth in the testes as well as age-related changes in absolute and relative testicular asymmetry. The left testis had significantly higher weight, volume and relative weight than the right testis. Similarly, populations of round spermatids, type I spermatocytes, total germ cell, Sertoli efficiency, actual and apparent seminiferous tubular diameters and testicular sperm production were higher in the left than the right testis. Correlations between the left and right testicular gross anatomical and histological biometric traits were strong and positive. Left biased asymmetry was recorded in the Guinea Fowl. Absolute testicular asymmetry increased with age, but tended to stabilise from 20 weeks of age, while relative testicular asymmetry remained stable throughout. Both absolute and relative testicular asymmetries were higher in breeding than non-breeding males. Compensatory growth was recorded in both testes with no difference in the degree of compensation. The left biased asymmetry observed in the Guinea Fowl was reflected in functional differences between the two testes.

Sperm flow cytometric parameters, antioxidant status, and testicular histomorphology in roosters fed diets supplemented with camphor

“…According to previous reports, the right testis is about 10% smaller than the left side ( Sun et al, 2019 ). The testicular asymmetry phenomenon ( Abdul-Rahman et al, 2018 ) was also observed in our study. Similar to our findings, Talebi et al (2018) reported that roosters with higher testes weight were better at sperm quality compared to other roosters.…”

Consequences of advanced maternal age on reproductive investment by male offspring

“…In many species, older males have larger testes because they have reached sexual maturity, and there is also some evidence for an increase in asymmetry between testes with age (Merila and Sheldon 1999, Brown and Brown 2003, Abdul-Rahman et al 2018. Perhaps the pattern of old males having smaller testes reflects a trade-off between reproduction and longevity (Austad and Hoffman 2018); if older males have invested more resources in survival and maintenance than younger males, this investment could come at the expense of reproductive somatic tissue.…”

Cemani chicken: characteristics of fresh semen, testes morphometric, and the relationship between the two traits

“…In addition to their length, the width of the left and right testes in Cemani chickens has been observed to exceed that of Sentul chickens [11]. On the contrary, an examination of the average weight of the left and right testes in Cemani chickens reveals a lower value compared to the naked neck and curly hair in the Southern Guinea Savanna region of Nigeria [30]. However, a higher value compared to Sentul chickens [11].…”

“…However, a higher value compared to Sentul chickens [11]. A change in our attention is directed towards another type of bird, as an investigation has unveiled that in the Guinea Fowl, the left testes show a magnitude that is roughly 10% larger than that of the right testes [30]. Testicular augmentation is regulated using photoperiod, nutrition, and gene expression, which subsequently modulate the hypothalamic-pituitary axis and initiate gonadal augmentation.…”