Alternative reproductive tactics and growth of male cunners, Tautogolabrus adspersus (Walbaum), in Newfoundland

Gravel, Carolyn Mary. (1987) Alternative reproductive tactics and growth of male cunners, Tautogolabrus adspersus (Walbaum), in Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Alternative reproductive tactics utilized in two separate populations of the Newfoundland male cunner, Tautogolabrus adspersus, were investigated for tradeoffs between sperm production and somatic growth. One population in Broad Cove, Conception Bay, consisted of pair spawning territorial males and nonspawning preterritorial males. A second population at Norris Point, Bonne Bay, contained group spawning nonterritorial males. The parameters measured from prespawning and postspawning samples of both populations were total length, eviscerated body weight, gonad weight, and age. These variables and a gonadosomatic index were tested for differences between the three reproductive types of males mentioned above. Results indicated that gonad weights and gonadosomatic indices per age class were significantly greater in group spawning males than in preterritorial males younger than 15 years. The same was found for gonad weight per unit body weight at age, thereby supporting the prediction that group spawners invest heavily in sex products early in life. Group spawning provides an opportunity for a female's eggs to be externally fertilized by many males, and large gonadal investments in group spawning males are probably a result of sperm competition. -- Length and body weight at age of the male group spawning population at Norris Point were significantly less than those of the preterritorial male population at Broad Cove. Body size differences were slight, however, suggesting no significant tradeoff between high sperm production and decreased somatic growth rate. A tradeoff between high sperm production and reduced longevity of group spawning males was suggested by the absence of older (> 9 years) males at the group spawning site (Norris Point) as compared to high frequencies of similar aged males at the pair spawning site (Broad Cove). Age frequencies of females were the same between both populations. -- Within the Broad Cove population, territorial males invested more energy in gonads than preterritorial males. Successful territorial males exhibited a faster growth rate than preterritorial males, although the maximum total lengths and body weights obtained were similar between both male types. -- Since female cunners exhibit the same growth and reproductive tactics irrespective of geographic location, differences in female body size at age were used to compare the conditions for growth between the two study sites. Norris Point females were significantly smaller in length and body weight at age than those of Broad Cove, although differences were slight. These observed differences in female body growth may be related to differences in local population density between both sampling sites. Females from both Broad Cove and Norris Point were smaller sized per age class than local males (excluding territorial males). They were also heavier at length than resident males, although differences were slight between sexes in Broad Cove. A comparison of the mean total lengths at age of cunners (sexes combined) with latitude from the literature indicated no readily apparent latitudinal effect on cunner growth.

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