The Searle lab focuses on the evolutionary biology of several species of small mammals as they are perfect for understanding how species evolve, colonize new areas, and adapt to the environment. Additionally, we use them as trackers of human history and as models for conservation.
Natural Colonization Adaptation and Speciation Human-Animal Relationships Conservation Genetics

Natural Colonization

Fig 1 in Herman & Searle 2011Small mammals may not seem to move very fast or very far, but they have colonized continents in just a few thousand years! Populations were contracted into refugia only 11,000 years ago because of glacial conditions, and have expanded out since then.

Genetic markers are being used in the lab to infer localizations of refugia and subsequent colonizations of Europe by shrews, voles and field mice. A diverse evolutionary history is evident. For example, field voles colonized Europe from many small refugia. Pygmy shrews, despite being incredibly tiny, lived in a cold part of central Europe during glacial conditions, then colonized much of Eurasia from there.

Adaptation and Speciation

Fig. 1 in Pavlova et al. 2008There are some small mammals that can cope with extraordinary environmental conditions. The American red squirrel, for example, stays active during harsh climate, either extremely hot or cold. Next-generation sequencing methods and gene expression studies via RNA-sequencing are being used in the lab to understand the genetic basis of adaptations in a physiological context.

Speciation is another focus in the lab with studies on mice and shrews where a different set of chromosomes may lead to new species. Genomic methods are being used to analyze genetic changes and cell biological methods applied to understand the chromosomal processes that lead to speciation.

Human-Animal Relationships

Small mammals have sometimes been able to travel incredible distances as unwanted guests on boats. House mice have been spread globally by humans and molecular markers can be used to track their movement. Once it is known where house mice came from and went to, it can be assumed that the people who unintentionally took them made the same journey. Thus, we are using house mice to tell us about human history, including prehistoric movements around the Indian Ocean, and Viking colonization history. We are also using house shrews; and particularly house/sewer rats for their role in pathogen transfer.

Fig. 3 in Jones et al. 2012

In addition, DNA and morphological studies of both modern and archaeological specimens have helped us study a Neolithic colonization of voles, and has even been applied to learning more about the domestication history of geese.

Conservation Genetics

Evidence of small mammals is easily obtainable, directly through live-trapping or indirectly via feces and hair collections, and DNA can be extracted from these various sources. Through genomic methods, we have studied endemic small mammals in Mexico and Iberia, and voles and shrews in Alaska, to understand the impacts of habitat disturbance on genetics. The work in Alaska is part of a broader study examining how conifer die-off is influencing wildlife communities and human health.

Small mammals may be models of species at conservation risk, but also models of conservation threats. Applying genomic methods to study invasive species – the bank vole and the greater white-toothed shrew in Ireland – have informed us about the invasion process through comparison of the genetic makeup of populations at the invasion front with those in more established populations near the invasion point.

 Image Sources (top to bottom): 1. Fig. 1 in Herman & Searle 2011; 2. Fig. 1 in Pavlova et al. 2008; 3. Fig. 3 in Jones et al. 2012

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