First Evidence of a Relationship Between Female Major Histocompatibility Complex Diversity and Eggshell Bacteria in House Sparrows (Passer domesticus)

Alžbeta Darolová,Barbara Lukasch,Miroslav Poláček,Ján Krištofík,Herbert Hoi

doi:10.3389/fevo.2021.615667

Abstract

Bacteria are known to exert positive and negative influences on animals’ health and fitness. Bacteria, in particular those inhabiting the skin and inner organs of vertebrates, are horizontally or vertically transmitted. Specifically, mothers of bird species can transfer bacterial strains to their offspring when the egg is passing the reproductive tract, as the eggshell rubs against the wall of the uterus. In this context, the female immune system might play an important role in influencing the vertical transmission of bacteria. Here, we investigate the relationship between the major histocompatibility complex (MHC) and cultivable eggshell bacteria originating putatively from the female urogenital tract in a captive population of house sparrows (Passer domesticus). We predict that females with a more variable MHC will transfer fewer bacteria onto the eggshells. Our results show a negative relationship between the number of functional MHC class I alleles and bacteria originating in the urinary tract and growing on a selective medium. This is the first study to find a correlation between female MHC diversity and eggshell bacteria.

Highlights

Animal health is significantly influenced by bacteria (Org et al, 2015)
When examining major histocompatibility complex (MHC) diversity in terms of the number of functional alleles in relation to the general bacterial numbers, we found no significant effect (Table 1a and Figure 1A, pseudo-R2 = 0.19)
The female body condition did not influence bacterial numbers at all; there was a significant seasonal effect, namely that bacterial numbers increase with time during the season (Table 1)

Summary

Introduction

Animal health is significantly influenced by bacteria (Org et al, 2015). The bacteria an individual harbors can be due to (i) horizontal transmission, which means they are spread from host to host in the same generation; or (ii) vertical transmission, which means they are spread between generations, namely from parents to offspring; or (iii) the host bacteria can originate from the environment.Bacterial communities can help during digestion, e.g., extracting energy and nutritional compounds (Hooper and Gordon, 2001; Ley et al, 2008), producing vitamins (Hill, 1997), or teaching and training the host immune system (Cebra, 1999; Macpherson and Harris, 2004). MHC Diversity and Eggshell Bacteria found in the reproductive system, are known to be vertically transmitted to the host’s offspring (Ruiz-de-Castañeda et al, 2011a; Tangkham et al, 2016; You et al, 2019). Early contact of offspring with bacteria occurs in the ovary and the oviduct of the mother. This happens either before oviposition, through direct contamination of the yolk, albumen, or eggshell membranes (Timoney et al, 1989; Keller et al, 1995; Okamura et al, 2001a,b), or during oviposition, when the egg is squeezed through the gastrointestinal system of the mother (De Reu et al, 2006; Messens et al, 2007). Contact with bacteria occurs after oviposition, with bacteria from the surrounding environment, e.g., airborne bacteria (Kulkarni and Heeb, 2007; Goodenough and Stallwood, 2012), or bacteria from the nest material or the parent surface (skin and feather bacteria)

Methods

Results

Conclusion