08-16-2005, 03:09 AM
The discussion about bluegills last week caused me to think about an interesting subject I studied back in the undergraduate days,in an upper division ecology/evolution class I took. The original scientific paper is here.
[url "http://www.pnas.org/cgi/content/abstract/77/11/6937"]LINK TO ARTICLE[/url]
One of the authors, Dr. Charnov was one of my instructors at the U. Anyway, the paper discusses that there are two "life histories of male bluegills. The main one is the "typical" pattern where the males grow for up to 7 yrs, grow to large (for a gill) size, and fight and defend nests, while encouraging females to lay their eggs in their nests for fertilization. Numerically, these are the most common, and what we are used to catching. The alternative is where it gets interesting. These are called "cuckolders". They are sexually mature at only 2 yrs. They do not grow to the size of typical males, and have external female characteristics. What they do reproductively is sneak in and out of nests made by "typical" males and when the male isn't watching, fertilizes the eggs in the nest. Cuckolders do not in time become "typical" males. It is an example of a type of parasitism involving a single species. If you catch a "female" looking gill that leaks milt on you it is a cuckolder.
One other topic that came up, which I thought I might elaborate on, is the phenomenon of selection pressure. It was brought up (correctly) that fishing typically exerts a selective pressure against large size because the typical angler wants a "big one". There is more to consider though when doing a selection problem. I came up with 3 more pressures in the example of gills. (There may be more) 1. Fish predation; Smaller sized fish are more prone to fish predation, so the selection "pressure" favors larger gills, IF there are predatory fish (ie big bass) in a fishery. 2.Bird and other predation; Pelicans will eat any sized gill, but terns, grebes, and cormorants probably eat more small fish so the "pressure" is toward larger size here. 3. Breeding success; A larger male gill will be better able to defend a nest, and fertilize larger quantities of eggs, so the "pressure" here favors more size. The net result regarding size, or any other trait, is when you add up all of the pluses and minuses and get a net result. The final "result" will often change from time to time depending on changes in the many factors.
I hope this wasn't intolerably boring, but I had fun dredging this up from my mushy grey matter, and having a flash or nostalgia from the old college days. Tight lines all.
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[url "http://www.pnas.org/cgi/content/abstract/77/11/6937"]LINK TO ARTICLE[/url]
One of the authors, Dr. Charnov was one of my instructors at the U. Anyway, the paper discusses that there are two "life histories of male bluegills. The main one is the "typical" pattern where the males grow for up to 7 yrs, grow to large (for a gill) size, and fight and defend nests, while encouraging females to lay their eggs in their nests for fertilization. Numerically, these are the most common, and what we are used to catching. The alternative is where it gets interesting. These are called "cuckolders". They are sexually mature at only 2 yrs. They do not grow to the size of typical males, and have external female characteristics. What they do reproductively is sneak in and out of nests made by "typical" males and when the male isn't watching, fertilizes the eggs in the nest. Cuckolders do not in time become "typical" males. It is an example of a type of parasitism involving a single species. If you catch a "female" looking gill that leaks milt on you it is a cuckolder.
One other topic that came up, which I thought I might elaborate on, is the phenomenon of selection pressure. It was brought up (correctly) that fishing typically exerts a selective pressure against large size because the typical angler wants a "big one". There is more to consider though when doing a selection problem. I came up with 3 more pressures in the example of gills. (There may be more) 1. Fish predation; Smaller sized fish are more prone to fish predation, so the selection "pressure" favors larger gills, IF there are predatory fish (ie big bass) in a fishery. 2.Bird and other predation; Pelicans will eat any sized gill, but terns, grebes, and cormorants probably eat more small fish so the "pressure" is toward larger size here. 3. Breeding success; A larger male gill will be better able to defend a nest, and fertilize larger quantities of eggs, so the "pressure" here favors more size. The net result regarding size, or any other trait, is when you add up all of the pluses and minuses and get a net result. The final "result" will often change from time to time depending on changes in the many factors.
I hope this wasn't intolerably boring, but I had fun dredging this up from my mushy grey matter, and having a flash or nostalgia from the old college days. Tight lines all.
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