Research published in the journal Nature Communications, led by the University of Bath, reveals that mammals with more developed brains show less difference in size between males and females. In many mammals, males are usually larger than females, a phenomenon known as sexual size dimorphism (SSD). For example, male elephant seals are three times larger than females, while dolphins show no size difference between the sexes. Humans are somewhere in between, with average males being larger than average females but with overlap within the population.

To understand how SSD is related to the evolution of the genome, scientists from the Milner Centre for Evolution at the University of Bath analyzed similarities between the genomes of 124 mammal species. They grouped genes into families with similar functions and measured the size of these gene families. They found that species with large differences in size between sexes have larger gene families associated with the sense of smell and smaller gene families associated with brain development.

Impact of SSD on gene families
Scientists discovered that species with large SSD have expanded gene families for olfactory function. Conversely, the gene families that shrank were associated with brain development. This may imply that species with small SSD have larger gene families related to brain function and more complex behaviors such as biparental care and monogamous mating systems.
Complex social structures and evolution
In species with smaller SSD, complex social structures allow competition for mates using methods other than size. Dr. Benjamin Padilla-Morales from the Milner Centre for Evolution at the University of Bath stated: "We were surprised by the strong statistical correlation between large SSD and expanded gene families for olfactory function. Even more interesting, the gene families that shrank were associated with brain development."

These findings suggest that species with small SSD, which have larger gene families associated with brain function, exhibit more complex behaviors such as biparental care and monogamous mating systems. It shows that while size is an important factor in sexual selection for evolution in some species, it is not as significant in others.

Questions for further research
Researchers plan to further investigate how testis size affects the evolution of the mammalian genome. Scientists from the University of Bath and Sheffield, Cardiff University, and UNAM (Mexico) and Universidad de las Américas Puebla (UDLAP) participated in the study.

This study contributes to a better understanding of how sexual size dimorphism can impact genetic diversity and the evolution of complex behaviors in mammals. The results open new questions about the role of size and brain functionality in the evolution of different species. The study was published in the journal Nature Communications.

Source: University of Bath