Fatal before fertilization?

Cecilia Bueno, Lewis & Clark College

frog calling

Male Squirrel Treefrog (Hyla squirella) calling for a mate (credit)

Amphibians, including frogs, toads, salamanders, newts, and others, are experiencing large declines in populations worldwide1. Many factors human-caused factors are contributing to this decline, including habitat loss, to climate change, and pollution1.

One way that habitats are being damaged is by increased salinity in normally freshwater systems. Salt is getting into freshwater by use of salt road deicers, poor land irrigation, rising tidelines, and increased storm surges2. Changes in water quality, such as salinity, is especially dangerous to amphibians such as frogs because of their permeable skin.

green treefrog amplexus

Breeding pair of Green Treefrogs (Hyla cinerea) in amplexus (credit)

In addition to increased salt levels harming adult frogs, it can damage developing frogs from fertilization onwards. Almost all frogs are external fertilizers- that is, when they breed, male and female join in amplexus and release sperm and egg into the water. Frogs require freshwater to breed and develop as tadpoles, so when freshwater is intruded by salt, there are problems for frogs from their earliest stages.

Many studies have shown that even low levels of salinity can cause tadpoles to develop abnormally, have lower adult weights, and die.While we already know that increased salinity has a bad effect on tadpoles, little is known about how this salinity affects frogs at the first stage of life: fertilization.

frog egg development

First stages of embryonic development (credit)

 

We hope to look at the effects of salinity on sperm and fertilization, an area which has very little research currently. Previous research has shown that in squirrel treefrogs, low levels of salinity can stop eggs from being fertilized4. A study on green treefrog sperm showed that as salinity increased, sperm function decreased incrementally5. These two closely related species live in the Coastal Plains habitat, which is at risk of salinization by rising tides and storm surges. Sperm function and fertilization rates have been shown to be negatively by increased salinity- we look at these two effects in squirrel treefrogs and see if a decrease in sperm function can explain at least part of how salinity hinders fertilization.

I would like to thank the National Science Foundation for funding this REU program, and the Grice Marine Lab of the College of Charleston for hosting us. In particular, I would like to thank my mentor Dr. Allison Welch for her help and support.

References:

1:http://www.amphibiaweb.org/declines/declines.html

Stuart, S. N., J. S. Chanson, N. A. Cox, B. E. Young, A. S. L. Rodrigues, D. L. Fischman, and R. W. Waller. 2004. Status and trends of amphibian declines and extinctions worldwide. Science 306:1783–1786. CrossRefPubMed

2: Williams, W. D. 2001. Anthropogenic salinisation of inland waters. Hydrobiologia 466:329–337. CrossRef

Van Meter, R.J., Swan, C.M., Leips, J. et al. (2011) Salinity Acclimation Affects Survival and Metamorphosis of Crab-Eating Frog Tadpoles. Wetlands, 31: 843. doi:10.1007/s13157-011-0199-y

3:Alexander, Laura G., Simon P. Lailvaux, Joseph H. K. Pechmann, and Philip J. DeVries. “Effects of Salinity on Early Life Stages of the Gulf Coast Toad, Incilius Nebulifer (Anura: Bufonidae).” Copeia 2012, no. 1 (2012): 106-14. http://www.jstor.org/stable/41416605

Brown, Mary E., Walls, Susan C. (2013). Variation in Salinity Tolerance among Larval Anurans: Implications for Community Composition and the Spread of an Invasive, Non-native Species. Copeia, Sep 2013 : Vol. 2013, Issue 3, pg(s) 543-551 doi: 10.1643/CH-12-159

4:Unpublished data, Ruby and Welch

5: Wilder, Anneke E., Welch, Allison M. (2014). Effects of Salinity and Pesticide on Sperm Activity and Oviposition Site Selection in Green Treefrogs, Hyla cinerea. Copeia, 2014, No. 4, 659–667

 

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