In the last 500 years, house mice have made themselves at home across the Americas. During this time, they have shown remarkable adaptability. One of the most noticeable changes is in their body size. This shift is not just about genetics. The environment, especially what they eat, plays a big role.

Scientists have been studying how genes and environment interact to cause these changes. They used mice from different parts of the Americas. These mice had adapted to their local environments over generations. The researchers wanted to see how these mice would react to a high-fat diet. They found that the mice's response varied greatly. Factors like sex, the specific strain of mouse, the diet, and the mix of strain and diet all played a part in how the mice's body size changed.

The study also looked at how the mice's genes responded to the diet. It turned out that each strain of mouse had its own unique response. This shows that gene-environment interactions affect how genes are expressed. In other words, the environment can turn genes on or off, leading to different traits.

Next, the scientists crossed mice from different climates. They wanted to see how gene expression changed on a standard diet and a high-fat diet. They found that many of these changes were specific to the diet. This means that the environment can influence which genes are active. This is especially true for genes that control other genes, known as trans-acting genes.

The study also found evidence of selection on genes that control how other genes are expressed. These genes are involved in various processes, including how the body handles fats. Some of these genes overlapped with those found in previous studies on adaptation. This suggests that these genes might be key to how mice adapt to their environment, especially when it comes to diet.

The findings highlight the importance of considering both genes and the environment. They show that complex traits, like body size, are shaped by a mix of genetic and environmental factors. This is a critical point to understand. It is not just about the genes an organism has, but also about how those genes interact with the world around them.

Mice in the Americas: How Food and Genes Shape Size

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