Until now little has been understood about the genetic
variations of terrapin turtles. Terrapins have been designated a species of
special concern in some areas and not in others. They are listed as an endangered
species in Rhode Island and threatened in Massachusetts. Terrapins are the only
North American turtle that spends its entire life in coastal marshes and
mangroves.
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Seven different subspecies of terrapins are
currently recognized by scientists based on external traits, such as their skin
color and the shape of their shells. Each subspecies occupies a strip of the
eastern seaboard or Gulf of Mexico coastline, from as far north as
Massachusetts to as far west as Texas.
Each subspecies occupies a distinct coastal
habitat sometimes defining its unique genetic variation.
“Before now, it was not clear how terrapin
genetics varied across the range,” said Kristen Hart, a USGS ecologist and lead
author of the study. “Understanding this variation across the landscape helps
land managers develop conservation plans. For example, they may pinpoint areas
where habitat protection can be supplemented with migration corridors.”
Agencies often maintain migration corridors to
help wildlife continue to breed based on their historic patterns. These are
areas where habitat restoration, regulatory policies, or other means are used
to ensure animals can pass safely between two or more prime areas of habitat.
Well-placed corridors could maintain the terrapins’ existing natural diversity
and keep their overall population numbers robust, explained Hart.
“Diversity loss can be a silent threat to many
species,” explained Maggie Hunter, a USGS research geneticist and co-author of
the study. “The threat to long-term survival of terrapins occurs if they become
separated into isolated groups. Isolation can affect their overall survival
several generations down the line.”
To support a healthy mix of genetic
diversity, however, managers must first understand the existing genetic
variation.
“Healthy interbreeding doesn’t mean that turtles
from Maine have to interbreed with those from Texas,” explained Hunter. “Once
managers know where ‘natural breaks’ in populations occur, they can focus on
keeping terrapin populations healthy by enabling reproduction within each of
those distinct groups.”
To identify those natural genetic breaks, Hart
teamed up with Hunter and USGS research geneticist Tim King to study their
breeding patterns using DNA from the blood samples of nearly a thousand
terrapins. Based on their variation in 12 genetic markers, strands of DNA
that King had decoded for comparative purposes, the terrapins were assigned
into genetically similar groups.
They found only 4 genetically distinct
populations, which came as a surprise; given there are 7 recognized terrapin
subspecies. This means the ‘natural breaks’ in breeding don’t correspond to the
ranges of those subspecies.
Read more at USGS.
Diamondback
Turtle image via Shutterstock.