Selected elements in Lake Michigan round goby (Neogobius melanostomus) reproductive physiology: spawning effort and determination of reproductive status of females and sperm competition in two reproductively distinct male morphs
Kline Brussee, Meghan
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https://hdl.handle.net/2142/50570
Description
Title
Selected elements in Lake Michigan round goby (Neogobius melanostomus) reproductive physiology: spawning effort and determination of reproductive status of females and sperm competition in two reproductively distinct male morphs
Author(s)
Kline Brussee, Meghan
Issue Date
2014-09-16
Director of Research (if dissertation) or Advisor (if thesis)
Czesny, Sergiusz J.
Department of Study
Natural Res & Env Sci
Discipline
Natural Res & Env Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
round goby
reproduction
reproductive physiology
oocytes
spawning effort
sperm competition
neogobius melanostomus
Lake Michigan
Gonadosomatic Index (GSI)
male alternative reproductive tactics
invasive species
Abstract
The round goby (Neogobius melanostomus) is a species within a large, tolerant, prolific family of fishes, Gobiidae, and has successfully invaded the Laurentian Great Lakes over the past two decades. Among the many reasons for their success are physiological factors that allow round goby to rapidly expand their range. Although much research has explored ecological impacts and behavior of round goby, their basic reproductive biology and physiology in invaded systems is understudied. This study evaluated spawning effort and determination of reproductive status of female round goby and sperm competition in two alternative reproductive tactics of male round goby in southwestern Lake Michigan.
Spawning peaks differed between two relatively proximate sites and occurred at 14-17°C. Peak spawning effort as determined by Gonadosomatic Index (GSI) score correlates with the highest proportions of mature oocytes and is indicative of oocyte turnover. This confirms the usefulness of GSI as a good indicator of spawning activity. Monthly egg counts were largely unchanged throughout the reproductive season (May-September) confirming continuous development and maturation of oocyte batches during a protracted spawning period. Significant differences in proportional oocyte counts per sample period were present for stage 1 (immature) and stage 3 (mature) oocytes, which aids in validation of predicted spawning peaks from GSI scores. An almost ubiquitous standard of GSI>8% is currently used to determine mature reproductive status in round goby but has remained unverified until recently (Zeyl et al., 2014). Our data showed that mature, “ready-to-spawn” female GSI scores are significantly higher than 8 and the GSI scores of non-reproductive and reproductive females differ significantly. However, the GSI scores of mature females with vitellogenic eggs that are not fully mature were significantly less than 8% suggesting that a more conservative standard might be appropriate depending on the question of interest for researchers and managers. Fecundity was significantly positively related to total length and total weight of individual females.
To examine sperm competition in the round goby, a suite of morphological measures and body condition indices were used to evaluate the potential for two male alternative reproductive tactics. Two distinct male morphs were confirmed in these populations: a sneaker male tactic and a parental male tactic. Parental males were larger, older, and dark in coloration with higher relative investment in seminal vesicle mass, approximately equal investment in seminal vesicle mass and testes mass, and lower GSI scores. Sneaker males were smaller, younger, and mottled in coloration with higher relative investment in testes mass, a nearly ten-fold higher investment in testes mass than seminal vesicle mass, higher relative papilla length, and higher GSI scores. Age of these male reproductive morphs was examined to determine the potential for flexible tactic expression, via ontogenetic shift, versus fixed tactic “choice.” There is evidence of an ontogenetic shift between these two morphs with smaller, younger males employing the sneak tactic and later transitioning to the parental tactic as they grow larger and older.
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