Sex Ratios and Sexual Dimorphism Among Recently Transformed Sea Lampreys, Petromyzon marinus Linnaeus

Abstract

The sex, length, and weight were determined of nearly all recently transformed sea lampreys migrating downstream in the Carp Lake River, Michigan, in the fall, winter, and spring of 1960–61. Similar data were collected from samples of an earlier run in the Carp Lake River and of runs in three other tributaries of Lakes Huron and Michigan. The sex ratio of the 1960–61 migrants in the Carp Lake River was 324 males:100 females. Sex ratios of migrants in the other runs varied from 77 to 86 males:100 females. The high proportion of males in the 1960–61 run in the Carp Lake River is attributed to the effective prevention of recruitment of sea lampreys in the river and transformation of the females at an earlier age than is characteristic of the males. A near equal sex ratio among recently transformed migrants is considered normal for the species. The sex composition of a run changed during the period of migration. The proportion of males among the migrants was greatest at the beginning of the run and declined steadily thereafter. The average size was smaller for males than for females. Differences in the mean lengths and weights of the sexes were statistically significant. The length–weight relation differed for the sexes and showed a slower rate of increase of weight with increase in length than is characteristic of other stages of the animals' life cycle. Seasonal changes in the length–weight relation had a trend toward lower weights among the migrants coming downstream in the later months of the run.

Growth of the Mountain Brook Lamprey Ichthyomyzon greeleyi Hubbs and Trautman

“…Differential rates of growth between sexes were not observed for larval I. greeleyi but have been reported for several species including P. marinus (Applegate and Thomas, 1965;Purvis, 1979), I. fossor (Purvis, 1970), L. fluviatilis and L. planeri (Bird and Potter, 1979). Most metamorphosing female I. greeleyi were longer and heavier than males, almost certaintly the result of one additional year as larvae rather than faster growth.…”

Novel perspectives in sexual lability through gonadal biopsy in larval sea lampreys

“…Concurrent with a reduction in sea lamprey numbers due to control in the Great Lakes, was a drastic shift in sex ratio. Adult males averaged 70% of the population prior to the onset of population control, however their numbers dropped to c. 40% in the years following (Applegate & Thomas, 1965;Smith, 1971;G. Klar, pers.…”

Age, growth, and sex ratio among populations of least brook lamprey,Lampetra aepyptera, larvae: an argument for environmental sex determination

“…Alternatively, it could be that the disproportionate percentage of males at spawning was artifactual, due either to small samples sizes or to the time or location of collection. Lamprey sex ratios, for example, have been shown to fluctuate during the spawning season (Zanandrea 1951, Hardisty 1961b, Stier & Kynard 1986, and may be attributed either to differential migration rates between the sexes (Applegate & Thomas 1965) or shorter female residence time on the spawning grounds (Farlinger & Beamish 1984). A better understanding of the relationship between larva and adult sex ratios is crucial to further hypotheses regarding the evolutionary significance of environmental sex determination in lampreys.…”