The impact of diet quality on the velocity, morphology and normality of sperm in the zebra finch Taeniopygia guttata

Abstract

Sperm traits can influence fertilisation success, but there is still much we do not understand about sperm condition dependence, that is, how much sperm traits depend on the male's energy acquisition and allocation. This is especially pronounced in avian taxa, despite extensive observational studies and sampling in wild populations. In this study we collected sperm samples before and after experimentally reducing diet quality of wild-derived captive zebra finches in small mixed-sex groups, which we compared to individuals on a control diet. We measured the length of sperm components (head, midpiece, flagellum and total sperm length), the proportion of sperm with normal morphology, the proportion of sperm that were progressively motile, and swimming velocity (curvilinear velocity; VCL). The only sperm trait we found to be impacted by reduced diet quality was a significant decrease in sperm midpiece length. This is consistent with emerging evidence in other non-model systems, as well the fact that diet can alter mitochondrial density and structure in other tissue types. There was also a significant decrease in sperm velocity and the proportion of motile sperm over the course of the experiment for both experimental groups (i.e. unrelated to diet). That in the control group experienced this decrease in sperm velocity was marked by no change in any sperm morphological measure highlights the existence of other important determinants of sperm velocity in passerine birds, likely including variation in other components of the seminal fluid.

Flagellum tapering and midpiece volume in songbird spermatozoa

“…It is therefore unclear how midpiece length relates to mitochondrial volume in general across Passerides songbirds. Many studies have investigated how the length of the midpiece and/or flagellum correlate with swimming speed, but no general pattern has been found in Passerides songbirds (e.g., Cramer et al, 2015 ; Cramer, Garcia‐del‐rey, et al, 2021 ; Helfenstein et al, 2010 ; Immler et al, 2010 ; Kleven et al, 2009 ; Lüpold et al, 2009 ; McDiarmid et al, 2022 ; Rojas Mora et al, 2018 ).…”

Experimentally testing mate preference in an avian system with unidirectional bill color introgression

“…These red and yellow nail polish colors were selected as they appeared to be the closest match to the bill colors of each subspecies by the human eye. To assess how effective our bill manipulations were we used reflectance spectrophotometry to measure bill color of both unmanipulated individuals and individuals with manipulated bills, following published protocols (Griffith & Hooper, 2017 ; McDiarmid et al, 2022 ; van Rooij & Griffith, 2012 ). Spectral reflectance of the center of the upper mandible was recorded three times using a USB2000 + Miniature Fiber Optic spectrophotometer (Ocean Optics Inc., Dunedin, FL, USA), a xenon light source PX‐2 (Ocean Optics Inc.) with a fiber‐optic cable held at an angle of 90° to the bill and about 10 mm from the surface of the mandible with a plastic sheath that excluded ambient light.…”

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

“…To measure bill colour we followed published methodology using spectrophotometry (Griffith and Hooper, 2017, McDiarmid et al 2022). Briefly, we made three consecutive measurements of spectral reflectance of the centre of the upper mandible using a USB2000+Miniature Fiber Optic spectrophotometer (ocean Optics Inc., Dunedin, FL, USA) and a xenon light source PX‐2 (Ocean Optics Inc.).…”

“…A powerful approach to research the condition dependence of male ejaculate traits is to modify nutritional intake (Macartney et al 2019), which has only been applied to just one species of a bird to date; the zebra finch Taeniopygia castanotis . One experiment in the zebra finch tested the impact of diet on sperm phenotypes (including sperm morphology; McDiarmid et al 2022), while an earlier study manipulated foraging effort and activity levels to assess condition dependence of zebra finch sperm traits (including total sperm length, but not the length of specific sperm components; Birkhead et al 1998), and another examined the impact of an experimental oxidative challenge and carotenoid supplementation on sperm morphology and velocity in the zebra finch (Tomášek et al 2017).…”

“…We wanted to expand our understanding of the impact diet can have on sperm morphology and use the long‐tailed finch Poephila acuticauda that is amenable to captive studies, facilitating the manipulation of diet. We followed a similar experimental protocol as a recent study on the zebra finch (McDiarmid et al 2022) by modifying diet and assessing sperm samples collected before and after the treatment. More specifically, we measured the length of sperm components before and after the experimental diet treatments for those who received a diverse diet (DD) and those who received a homogenous diet (HD).…”