Editor's note: This is the first in a series of guest columns provided by the local ACRES Land Trust regarding local nature topics. The columns are being provided as part of ACRES' 50th-anniversary observances. This column was written by
Trina Herber, a member of ACRES' Education Committee
.
In most cases, humans do not choose if their unborn child will be a boy or a girl. Such decisions are determined by genetics through direction of chromosomes and genes.
For some animals that lay eggs, the process of gender is not so cut and dry. Although the egg may have a certain genetic code, environmental factors like temperature or pollutants in water may influence whether the developing embryo ultimately becomes male or female.
For some reptiles, specifically most turtle species and all crocodiles, sex of the hatchling is determined by the incubation temperature of the fertilized egg. The snapping turtle, common to northeast Indiana and found in shallow ponds, lakes and streams, is one example. Snappers usually lay eggs in June and July with eight to 15 weeks of incubation. At temperatures of 72 degrees and below, or 82 degrees and above, eggs become females. Males, mostly, hatch from eggs that develop in temperatures in between.
The red-eared slider, a turtle frequently found in ponds and lakes in this region or as a household or classroom pet, is also affected by temperature, but in a different range and variation. Temperatures below 82 degrees yield males, while temperatures above 88 degrees yield females. Temperatures in between give rise to both sexes.
Special temperature requirements as seen in reptiles give scientists more reason to be concerned about the effects of seasonal weather trends and global warming. If seasonal temperatures increase enough, some species of reptiles may reach the brink of extinction if eggs hatch primarily as one gender and reproduction ends.
Other environmental factors besides temperature impact the sex of animal hatchlings. For example, some herbicides applied to farmland to kill weeds contain ingredients that have an unforeseen negative side effect — acting like sex hormones when they contact animals.
For example, in some fish eggs, the herbicides that run off farm fields into streams can diffuse through the egg surface and influence the sex of the developing fish. For herbicides that contain compounds capable of acting like estrogen (female sex hormone), the majority of the eggs exposed to the contaminated water may hatch as females. Additionally, male fish can be feminized to the point of sterilization.
Conversely, some common chemicals behave like testosterone (male sex hormone) and give the opposite effect — more males in a population, or females that are not capable of reproducing.
Nature preserves and other natural properties have little or no control over the pollutants that enter the property by water or air. Managers of these properties are not able to protect the balance of nature when residents or businesses upstream or upwind introduce contaminants.
