Darwin’s Postulates & Firemouth Cichlids

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This was a research project done in Evolutionary Biology (BIO405W) during the spring 2013 semester at Buff. State


Cichlid fish are one of the most biologically diverse groups of vertebrates on the planet. This diversity (as well as population size, reproduction rate, etc) allows scientists to study the cichlid evolution, and the role of natural selection, more closely than other populations. Many aspects of cichlid characteristics have undergone (and are currently undergoing) selective pressures. Cichlid evolution can be found at multiple levels, including behavioral changes, molecular adaptations, size and coloration variation.

Screen Shot 2014-07-24 at 10.42.50 AMThorichthys meeki is a species of cichlid commonly known as the “firemouth”, because of its bright red-orange coloration on the jaw. This specific coloration is unique to the firemouth, and is used in mating, competition and defense, and is therefore strongly affected by selective  pressures. In general, male firemouth cichlids have prominent  jawline coloration (10). The female Firemouth cichlids have specific molecular adaptations that that allow them to see the male coloration very clearly (6).

In the case of the firemouth cichlids, jawline coloration in males (and the subsequent female response) plays an important role in the evolution of the species due to the pressures of sexual selection. Sexual selection has been shown to be a mechanism of significant biological change for firemouth cichlids, even if the environment stays very stable (9), and research confirms that male coloration corresponds to sexual selection by the females (8). The females tend to mate with the more dominant males, so any characteristic that improves one’s chance of winning in a male-male competition scenario will be selected for. In any cichlid population, males who display the same color will compete more intensely. In firemouth cichlid populations, all of the males have a distinguishing red color, so male-male competition is very strong (4).

firemouthIt has been shown that smaller, less dominant males have physiological and behavioral changes during any social interaction with a more dominant cichlid. (3).  Many times, cichlids will engage in “pre-fight behaviors” (7) and  whichever male is smaller and duller will back down (5).    The coloration allows the more dominant males to emerge victorious from a fight with other males, without even having to engage in actual physical contact. The firemouth cichlids open their mouths and expose more of the red jawline. This behavior enlarges the head considerably when seen from the front and the side. In the event that there is no definitive pre-fight winner, they will engage in the more dangerous physical form of fighting. (1) In many cases, coloration is directly correlated to body size, which also plays a role in determining the winner of the conflict. (2) Read the rest of this entry »

The Responses of Anuran Species to Varying Levels of Ultra Violet (UV-B) Radiation

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Screen Shot 2015-10-05 at 4.24.08 PMUltra Violet Radiation and Its Role in Frog Ecology and Evolution
Ultra violet radiation, especially UV-B radiation (280 – 320 nm), has been hypothesized to be one of the major contributing factors to the decline of amphibian populations worldwide (Gardner 2001, Houlahan et al. 2000, Keisecker et al. 2001). UV-B radiation has been known to cause an increase in the likelihood of premature death, as well as malformations and deformations in a large number of frog (order Anura) populations (Han et al. 2007,  Keisecker et al. 2001, Blaustein et al 2003). While the exact effects UV-B  radiation has on frog development is currently being investigated and  debated,  many conclusions can be drawn from past and current  research. UV-B radiation  by itself is a known problem, but when  combined with other factors (pH,  temperature, water depth, mold) it can  cause a synergistic and additive effect  (Bancroft et al. 2008, 2nd  reference, Gardner 2001).

There has also been a variety of research investigating the role of physiological, molecular and behavioral (Han et al. 2007, Blaustein et al. 2003) adaptations in frog populations. These adaptations are in response to the recent increase in UV-B radiation on the surface of the planet, which has been caused by the recent decrease in stratospheric ozone (Bancroft et al. 2008, Diamond et al. 2002). In some cases, the size of the population may also have an influence the effects of UV-B radiation (Houlahan et al. 2000).

Effects of UV-B Radiation on Anuran species
Exposure to UV-B radiation can cause various types of lethal or sublethal effects on amphibians (Han et al. 2007). These effects include genetic deformations, improper development, various forms of skin malformations, and premature death (Diamond et al. 2002). Due to the recent decrease in stratospheric ozone and the decrease in surface water level in frog habitats, there has been a significant increase in the amount of exposure to UV-B radiation in frog populations (Bancroft et al. 2008).

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