Effects of social interaction on sex determination in Midas cichlids

A version of this document was originally presented as a poster at the University of Michigan's Young Scientist Symposium 2007.Juvenile Midas cichlids, Amphilophus citrinellus, have been reported to have sex determined by social factors. I observed behavior in, and histologically analyzed gonads of, specimens from nature and laboratory to determine the effects of behavioral interaction and relative body size on sex determination. Social conditions were found not to influence whether an individual differentiated as a female or a male.The University of Michigan and the American Cichlid Association provided funding.http://deepblue.lib.umich.edu/bitstream/2027.42/51525/1/OldfieldYoungSciPoster2007.pd

Fish species observed on the shipwrecks Regina and Sport in Lake Huron

http://deepblue.lib.umich.edu/bitstream/2027.42/51531/1/Oldfield_Amer_Curr_2006.pd

Saltwater cichlids. Knowledge of salinity tolerance and preference may allow new species combinations and improved husbandry in aquaria.

http://deepblue.lib.umich.edu/bitstream/2027.42/51532/1/Oldfield_Saltwater_Cichlids_2004.pd

Effects of group size, space, and 3-D structure on behavior in captive Midas cichlids

A version of this document was originally presented as a research poster at the Winter (Dec.) 2006 meeting of the Association for the Study of Animal Behaviour held at the London Zoo.Animals may perform elevated levels of aggression in captivity, which may be a response to the modified costs and benefits of resource defense imposed by their artificial environments. The Midas cichlid (Amphilophus citrinellus) is a species whose patterns of aggression appear to fit predictions of resource defensibility. Two experiments were performed to test the effects of small-scale changes in group size, available space, and habitat complexity on aggression to determine if juvenile Midas cichlids modify behavior under different conditions of defensibility. Proportions of time spent in aggression were not associated with group size or available space, but submissive behavior performed by subordinates and the amounts of body damage they received were. Aggression was lower in the presence of 3-D structure. Behavior in the experiments was then compared to that observed in a large zoo exhibit (large group size) and in nature (large available space) to investigate the effects of large-scale differences in defensibility. Aggression was highest under the more defensible, experimental conditions. Midas cichlids increased aggression under defensible conditions, but were unable to maximize net benefits by adjusting aggression according to fine-scale changes in defensibility in artificially small group sizes and enclosures, which resulted in aberrantly detrimental effects on subordinates. Captive aggression in the absence of food or mating motivation suggests that space was defended as a resource, but it may result as a default due to restrictive artificial conditions that do not provide opportunities for alternative activities. Regardless, it has serious animal welfare implications. Some alternative housing tactics that do not promote aggression may nevertheless be suboptimal as they restrict behavioral diversity.The University of Michigan and the American Cichlid Association provided funding.http://deepblue.lib.umich.edu/bitstream/2027.42/51526/1/OldfieldMidasGroupAggrPoster2006.pd

Biology, husbandry, and reproduction of freshwater stingrays

http://deepblue.lib.umich.edu/bitstream/2027.42/51533/1/Oldfield_Stingrays_2005.pd

Effects of Behavioral Interaction on Sex Determination in the Midas Cichlid.

Some teleost fishes can change sex according to social conditions, a trait that has been proposed to have evolved through a change in developmental timing. I reviewed literature and found that cichlids exhibit different expressions of lability at each of three life stages, supporting this idea. In Midas cichlids, Amphilophus citrinellus, relative body size within a group has been reported to determine sex at the juvenile stage, with larger individuals differentiating as males and smaller fish differentiating as females. In contrast to this report, I found that sex was not associated with either behavioral interaction or relative body size in any of 10 small groups of Midas cichlids that were grown to maturity in the laboratory. In Lake Apoyo, Nicaragua, large juveniles at the onset of sex differentiation exhibited no association between body size and sex in either of two natural social groups. In lab experiments that restricted available space and numbers of competitors, juveniles behaved territorially and performed elevated levels of aggression. Therefore, subsequent lab experiments tested the effects of relative body size on sex determination at larger group sizes and in larger tanks. When eight groups from four different lineages were grown for much longer periods, sex was unrelated to body size initially, but as the fish matured males began to grow faster than females. Maturation in isolation did not affect sex determination. Of 25 wild-caught Midas cichlids of various ages from the same locality as those used in the original reports, none had bisexual gonads although these are often present in sexually labile species. In juveniles, there was no significant difference in body size between females and males, but in adults males were much larger than females. In each investigation, results were not consistent with a hypothesis of socially controlled sex determination. Larger body size in adult males compared to adult females is attained not because the largest juveniles differentiate as males, but because males experience greater post-maturational growth than females. Sex determination in Midas cichlids therefore does not support any ypothesis regarding the evolution of functional sex change in sequentially hermaphroditic fishes.Ph.D.Ecology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/55671/2/roldfiel_1.pd

Chemical cues, 3-D structure, and social experience in contests between similarly sized juvenile black Midas cichlids, Amphilophus sp. ‘short’

This document is scheduled to be presented by the first author as a research poster at the 2007 meeting of the American Society of Ichthyologists and Herpetologists.Juvenile Midas cichlids are not territorial or remarkably aggressive under natural conditions but become extremely aggressive when placed in small aquaria. The potential effects of prior experience with 3-D structure, recent social interaction, and chemical cues on determining the outcome of contests between juvenile Midas cichlids were tested under laboratory conditions. Fish with a clay pot in their pre-test tanks defeated opponents without such prior experience when test tanks contained an identical pot. Experience in a small group of conspecifics had no significant effect on contest outcome, although fish that held lower size ranks tended to lose contests. Conspecific chemical cues did not affect the outcome of contests. Thus, although juvenile Midas cichlids are not typically aggressive they are sufficiently plastic not only to behave aggressively under certain conditions, but to adjust aggressive behavior according to prior experience with environmental structure as do some animals that are naturally territorial.The University of Michigan and the American Cichlid Association provided fundinghttp://deepblue.lib.umich.edu/bitstream/2027.42/51535/1/PriorExperMidasPoster.pd

Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73799/1/j.1467-2979.2005.00184.x.pd