The impact of diet on sperm length in the long-tailed finch (Poephila acuticauda)

Sperm traits are important in determining fertilisation success and are metabolically expensive to produce. There is little known about how energy acquisition and allocation affect sperm traits in avian taxa. This study assesses the impact of experimentally manipulated diet on long-tailed finch sperm by comparing the length of sperm components (head, midpiece, flagellum and total sperm) between the treatment groups (homogenous diet and diverse diet) and across time points (before and after the experiment). Diet homogeneity was manipulated as this may impact diet quality in a species that is usually fed a diversity of seed species to thrive in captivity. Our results showed no impact of diet on the length of different sperm components. These results contrast with findings of a similar recent study of the zebra finch which found a significant level of diet-affected plasticity in midpiece length. For both diet treatment groups in this study there was a slight but significant increase in head, flagellum and total sperm length over the treatment period. Despite this, all sperm components were highly repeatable, consistent with the finding from observational studies in passerine birds. The efficacy of our dietary manipulation was confirmed by a significant reduction in the saturation of bill colour in the long-tailed finches as a result of the homogenous diet, and a difference in body mass across the treatment groups.

Automated summary

This study assessed the impact of experimentally manipulated diet on the sperm traits of long-tailed finches. The results showed that diet had no significant impact on sperm length, in contrast to a study on zebra finches. However, there was a slight increase in head, flagellum, and total sperm length during the treatment period. The dietary manipulation also affected bill color saturation and body mass in the long-tailed finches.