Wednesday, March 9, 2016

Sneaky Female Mimicking Bluegill, by Don Orth

Don’t be fooled by a sneaky fish.  Life histories are not engineered nor created. Rather, life histories are a product of natural selection, which is sometimes disruptive.  Bluegill, Lepomis macrochirus, is a very popular, well-studied fish that is superbly adapted to many lentic habitats in North America; they naturally range widely from Texas and Florida into eastern Canada.  A Bluegill was the first fish I caught, cleaned, cooked, and ate. Bluegills are typically locally abundant because the female is extremely fecund.  Furthermore, the parental male provides care for the eggs and fry, reducing predation at this vulnerable life stage. Intense harvest on adult bluegill makes the truncated size-structure a pervasive management concern. But its harder to fix than you might think.
Bluegill as we want them. Male 10.5 inches.  photo by Jim Gronaw
Dr. Richard O. Anderson preached the gospel of managing for balanced fish populations in the 1970s when I was still in college.  His investigations demonstrated that Largemouth Bass, if protected from excessive harvest, could control the size structure of Bluegill populations.   His favorite line was “God must have loved the Bluegill; why else would he have made so many?” Reducing the daily bag limit from 25 to 10 could also improve the size structure of Bluegill in Wisconsin lakes (Rypel 2015).  There goes the popular myth that bag limits are not be effective.  For more about the harvesting Bluegill in pond management, read Anderson (2011).   This post is about the complexity in Bluegill life history.  Here’s a case where you cannot simply “do the math” and calculate effects of fishing. These fish are responding to selective pressure and there are many Bluegill phenotypes across the vast range of the species.   There are three types of male Bluegill – namely the parental male, sneaker male, and satellite male.    The sneaker and satellites are female mimics; their coloration resembles that of the female. They are patterned to deceive. 
Female mimic, parental male, sneaker male, and female Bluegill (Neff and Svensson 2013).
The parental male selects a nest site, constructs a circular depression, and courts a female.  The pair then releases gametes in the bottom of the circular nest depression and the male fans and guards the offspring.  That’s a lot of work!  And the Bluegill are promiscuous breeders.  The male Bluegills have alternative mating strategies that permit fertilizations.   These are sneaker and satellite males that avoid the work and steal fertilizations by fooling the parental males.  It’s called kleptogamy and those stealing fertilizations are cuckholders.   Sneakers and satellites pass on their genes at a much younger age.  Consequently, they are big testes in a small package.  
Alternative mating strategies in the Bluegill.
Dr. Derek Aday, now a Professor at North Carolina State, and his colleagues examined the role of the large male in creating more sneaker-type males.  Bluegill from populations with large parental males and stunted males were transferred to similar ponds to test for genetic and environmental effects.  The experiment also manipulated the social structure by controlling the presence or absence of large, mature, male bluegill.  If genetic differences were the dominant influence, then the source population effects would be most evident.  In these experiments, the differences in growth and maturation of small bluegill were small, but significant.  However, juvenile male bluegill from both populations allocated significantly more energy to reproduction in the absence of large males than in their presence.   Both genetics and social interactions of large males were at play here (Aday et al. 2008).
Sneaker male Bluegill, dissected to show testes. Photo by Wisconsin DNR.
Dr. Andrew Rypel, a fishery ecologist with the Wisconsin Department of Natural Resources, wrote that “The lack of life history data on parental and sneaker male Bluegills and how these strategies respond to various fishing regulations also represents a key gap in knowledge...”   I cannot believe I am writing this statement -- but, it appears that more research on Bluegill is needed!   The Bluegills are able to discern just how promiscuous their mating has been.  Males know it!  Yes, they can smell it! Chemicals are cues to nestling recognition by parental male bluegill (Neff and Sherman 2003).  In fact, the male spends more time in protective behaviors when the brood consists of more of his offspring.
Change in male parental investment in response to perceived paternity (Neff  and Gross 2001).
It matters who your parents were -- that seems obvious.  In the case of the Bluegill, if your male parent was a cuckholder, you are likely to be a larger fry and have a larger eye (Neff 2004).   Why?  What’s the advantage?  Many of the weedy habitats that Bluegill fry inhabit are filled with the cnidarian Hydra canadensis.  Hydra can prey on young Bluegill fry.  Therefore, the larger size and better vision (larger eye) greatly reduces predation by Hydra (Neff 2004).  Furthermore, the sneaker males confer genetic difference in early growth to their offspring.

The phenomenon of alternative mating tactics is not unique to the Bluegill.  It also occurs in Pacific Salmon (Oncorhynchus spp.), Atlantic Salmon (Salmo salar), as well as other animals. There are many questions remaining about the mechanisms for alternative mating systems.  Further, fisheries managers would like to know how to increase the number and size of parental male Bluegill, without having an explosion of small sneaker-sized Bluegill that will never grow up to an acceptable size for anglers. 

Fishing for Bluegill is the easiest type of fishing to do with kids. There are many easily learned options for bait, tackle, and techniques. Plus, the Bluegill is a great fish to eat and there are many ways to prepare your catch.   These sneaky Bluegill can be easy and fun to catch.  Take a kid fishing, for Bluegill!

Aday, D. D., J. J. Parkos, and D. H. Wahl. 2008. Exploring stunted body size: where have we been, what do we know, and where do we go? Pages 349–367 in M. S. Allen, S. M. Sammons, and M. J. Maceina, editors. Balancing fisheries management and water uses for impounded river systems. American Fisheries Society, Bethesda, Maryland.
Anderson, R.O. 2011.  Catch and release or selective harvest.  Pond Boss Magazine Online accessed March 8, 2016.
Gross, M. R. 1982. Sneakers, satellites and parentals: polymorphic mating strategies in North American sunfishes. Zeitschrift fur Tierpsychologie 60:1–26.
Miller, M.  2015.  Big battles, big gonads: The crazy world of the Bluegill spawn. Cool Green Science.  Online Blog   Accessed March 8, 2016.
Neff, B.D. 2001.  Genetic paternity analysis and breeding success in Bluegill sunfish (Lepomis macrochirus).  Journal of Heredity 92:111-119.
Neff, B. D. 2003. Paternity and condition affect cannibalistic behavior in nest-tending Bluegill sunfish. Behavioral Ecology and Sociobiology 54:377–384.
Neff, B.D. 2004. Increased performance of offspring sired by parasitic males in bluegill sunfish.  Behavioral Ecology 15(2):327-331.
Neff, B.D., and M.R. Gross. 2001. Dynamic adjustment of parental care in response to perceived paternity.  Proceedings of the Royal Society of London B 268:1559-1565.
Neff, B.D., and P.W. Sherman.  2003.  Nestling recognition via direct cues by parental male bluegill sunfish (Lepomis macrochirus). Animal Cognition 6:87-92.
Neff, B.D., and E.I. Svennson.  2013. Polyandry and alternative mating tactics. Philosophical Transactions of the Royal Society B 368
Rypel. A.L. 2015. Effects of a reduced daily bag limit on Bluegill size structure in Wisconsin lakes. North American Journal of Fisheries Management 35(2):388-397. DOI: 10.1080/02755947.2014.1001929

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