Abstract
The present study addresses the effect of heat stress on males' reproduction ability. For that, we have evaluated the sperm DNA fragmentation (DFI) by SCSA of ejaculates incubated at 37°C during 0, 24 and 48 hours after its collection, as a way to mimic the temperature circumstances to which spermatozoa will be subject to in the ewe uterus. The effects of temperature and temperature-humidity index (THI) from day 60 prior collection to the date of semen collection on DFI were examined. To better understand the causes determining the sensitivity of spermatozoa to heat, this study was conducted in 60 males with alternative genotypes for the SNP G/C−660 of the HSP90AA1 promoter, which encode for the Hsp90α protein. The Hsp90α protein predominates in the brain and testis, and its role in spermatogenesis has been described in several species. Ridge regression analyses showed that days 29 to 35 and 7 to 14 before sperm collection (bsc) were the most critical regarding the effect of heat stress over DFI values. Mixed model analyses revealed that DFI increases over a threshold of 30°C for maximum temperature and 22 for THI at days 29 to 35 and 7 to 14 bsc only in animals carrying the GG−660 genotype. The period 29–35 bsc coincide with the meiosis I process for which the effect of the Hsp90α has been described in mice. The period 7–14 bsc may correspond with later stages of the meiosis II and early stages of epididymal maturation in which the replacement of histones by protamines occurs. Because of GG−660 genotype has been associated to lower levels of HSP90AA1 expression, suboptimal amounts of HSP90AA1 mRNA in GG−660 animals under heat stress conditions make spermatozoa DNA more susceptible to be fragmented. Thus, selecting against the GG−660 genotype could decrease the DNA fragmentation and spermatozoa thermal susceptibility in the heat season, and its putative subsequent fertility gains.
Highlights
Increasing concern over the implications of Climate Change in biodiversity is clear
If maximum daily temperature-humidity index (THI) is considered, we found days from May to August in which this parameter was in the range of extreme heat stress
The present study shows how the exposure of males to heat has consequences on the spermatogenesis process that result in an impairment of sperm chromatin which could lead to subfertile events
Summary
Increasing concern over the implications of Climate Change in biodiversity is clear. Many efforts are intended to better understand such implications, which are reflected by the large number of studies about this topic developed in the last decade [1,2,3]. It is generally acknowledged that climate change has a wide-range of biological consequences, potentially leading to impacts on biodiversity. These biological effects are especially noticeable in areas with adverse environmental conditions, such as the arid regions of southern Europe, where temperature and humidity conditions are more extreme. In these areas an important farming activity takes place. Climate can affect in many ways animals’ ability to survive and to produce. In this context, breeding for heat stress tolerance is of interest
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