gistfile1.txt

1.	a)	The observation was that species radiations were most likely to occur in deep lakes and in regions 

with more incident sunlight, as well as older lakes. Also, species radiation also were more likely to occur in 

species exhibiting sexual dichromatism. The question posed, then, is that whether or not adaptive radiation can be 

predicted based on extrinsic and intrinsic factors.

	b)	The hypothesis is that adaptive radiation can be predicted if both intrinsic and extrinsic factors 

for a species are considered together.


2.	An intrinsic lineage-specific factor is a factor which is affected by the trait of a species, whereas an 

extrinsic environmental factor is a factor which is affected by the surroundings and the surrounding conditions of 

the species. An example of an intrinsic lineage-specific factor would be the presence of sexual dichromatism, while 

an example of an extrinsic environmental factor would be the amount of sunlight a lake receives.


3.	The African cichlids are a good model system because of their presence in many different environments in 

combination with a very diverse speciation which allows scientists to observe the effect of many different 

intrinsic and extrinsic factors and their interactions on adaptive radiation. The fact that cichlids have colonized 

many lakes, but have radiated in different degrees is a good model system for this study because the scientists can 

examine the difference in the factor variables and determine a correlation between the degree of radiation and the 

intrinsic and extrinsic factors.


4.	a)	In figure 1a, the authors were demonstrating the amount of adaptive radiation across the African 

cichlids, and their degree of radiation.
	
	b)	Molecular phylogeny is less error prone because for rapid radiation, sometimes phenotypic changes 

are non-obvious, which can lead to errors in constructing a morphological phylogeny, where as the molecular 

phylogeny deals with genotypic and molecular changes across the species, which would be more accurate as it is 

independent on the outward appearance of the species.


5.	Since the presence of radiation was treated as a boolean factor variable, changing the level at which the 

factor variable is changed will change the level of correlation, mainly that a more strict requirement (at least 5 

species) will result in a deflation of the relative importances, which is observed.


6.	a)	Sexual dichromatism can cause an allele of the females to only sexually select for a specific 

allele of the male, which over time, will lead to a diversification event.
	
	b)	Although polygamy seemed to be a prerequisite to strong sexual selection, it does not a 

characteristic of strong sexual selection. The intensity of sexual selection is highly correlated with speciation, 

but having a polygamous mating system is not indicative of strong sexual selection, thus it is not an important 

factor in predicting diversification events.


7.	An older lake indicates environmental stability and persistence, which are conducive to speciation, thus 

lake age is associated with adaptive radiation. A greater lake depth increases the habitat area, as well as 

creating more niches that allow multiple species to thrive.


8.	Geological locations around the equator receive more direct sunlight, and the inverse is true for areas 

near the poles. The authors identificed net solar radiation as a strong predictor of speciation in cichlids, which 

could explain this phenomenon.


9.	a.	Lake depth displays the most positive correlation.
	b.	Lake depth displays the most positive correlation.
	c.	It means that this factor variable is negatively correlated with speciation, an increase in this 

factor variable decreases the likelihood of radiation.


10.	Based on the results of this study, it is very possible for a species to be biologically predisposed to 

undergoing an adaptive radiation if it possesses intrinsic factors which facilitate speciation, such as sexual 

dichromatism, or haplochromine egg dummies. This probably means that for the great radiations in Earth's history, 

not only are the extrinsic factors conducive to speciation, the species which underwent great adaptive radiation 

most likely possessed these traits which made it more biologically predisposed to doing so.