Parental ecology of the plainfin midshipman (Porichthys notatus)
Statement of Problem
Systems with alternative reproductive strategies have one sex, which employs two or more different strategies to procreate with the other sex. A number of fishes have male alternative reproductive strategies known as sneakers. The plainfin midshipman's (Porichthys notatus) breeding system has parental males (Type I males) and sneaker males (Type II males). Parental males make nests under rocks in the intertidal zone, and attract females by making "humming" noises. Type II males attempt to snake into the nest while the female is spawning to steal copulations from the Type I male, who then takes care of the eggs after the female and Type II male have left.This system presents us with an opportunity to examine which nest site attributes sneaker males may be focussing on. Other well-studied breeding systems with sneaker males are colonial, and we can not decipher individual male preferences. The plainfin midshipman sneaker males, however, select specific nests with specific males in them, which enables us to examine which Type I male attributes sneakers may be selecting. I predict sneaker male preferences will mimic female midshipman preferences that have been found in previous studies. Sneaker male preferences will mimic female midshipman preference, because sneaker males can maximize fertilizations by doing so. I also predict that midshipman will be able to return to the same nest site year after year, and that there is a high cost associated with being a nest guarder (Type I male).
Sources of Data
This research was conducted in Tomales Bay, California from May 2006 through August 2007. All research was conducted on the extreme low tides of each month, to give access to the research sites. The data came from natural habitats (rocks) and artificial habitats at shores in the town of Marshall, California, and at Hearts Desire Beach in Tomales Bay State Park, California. Midshipman were found by overturning rocks in the low tide zone on these shores and were captured by hand. The rocks under which midshipman breed occur in the low tide zone which is only accessible when the tide is out and is below roughly -0.2m mean water level. Sampling time increases the lower the tide recedes, however, abiotic factors can alter tidal height.
To test the nest site size preference of Type II sneaker males, artificial habitats were created and placed at Hearts Desire Beach in Tomales Bay State Park. Concrete slabs were put in place in March, 2007 and were checked during every low tide cycle between April, 2007 and August, 2007. All midshipman found in artificial and natural habitats were tagged using 10mm nickel monel tags. The specific nest number and size was recorded, along with the total and standard length of the fish, and the weight of the fish, whether embryos were present, and if the fish was found alone or with other midshipman. The sex and reproductive strategies of each fish was assessed and documented.
T-tests were conducted to determine if the means for the various nest site characteristics (Type I male size, new egg number, old egg number, total egg number, and nest size) were statistically different in nests where Type II males were present, versus nests where Type II males were absent. Data on nest site characteristics from days where Type II males were not found, were not analyzed, because it was unclear if a Type II male was in the area on these days, or if on that particular day all the Type II males in that area chose not to parasitize the nests on that shore. A goodness of fit test was used to see if females and Type II males co-occur in nests at a ratio that can not be explained by chance alone.
Nine nests that contained Type II males were found over the study period. The attributes of these nine nests were compared to the attributes of seventeen other nests that did not have Type II males present in them. The mean for the log of new egg number was significantly different between nests that contained Type II males versus nests that did not (Welch’s t-test assuming unequal variances). The mean for the log of total egg number was significantly different between nests that contained Type II males versus nests that did not (independent samples t-test).
Type II males are more likely to be found in nests that contain females. Type II male preference may or may not to be mimicking the female preferences found in previous work. The results of this study suggest that Type II males may merely be selecting for nests that have females in them, or have recently had females in them. No Type II males or females were recaptured after their initial tagging, suggesting that after spawning they leave the breeding grounds.
Of the 172 fish that were tagged in 2006, none were recaptured in 2007. The average Type I male spends 34 days engaging in spawning activities (creating a nest, attracting females, providing parental care, etc.) and loses on average over three percent of its body weight while providing care for the offspring. This suggests a high cost associated with being a Type I male. The longest time a Type I male was documented engaging in spawning activities was 131 days. Midshipman were documented breeding and guarding nests from March to the beginning of December with no evidence of spawning activity from January through February. These data indicate the plainfin midshipman’s breeding season lasts five months longer than previously documented.
Philllips, James Earl (2007) Parental ecology of the plainfin midshipman (Porichthys notatus). Masters thesis, Department of Biological Sciences, California State University, Sacramento.
James joined the lab in January of 2006 and finished in December 2007.