Kevin L. Teather

Developmental, behavioral, and reproductive effects experienced by Japanese medaka (Oryzias latipes) in response to short-term exposure to endosulfan.

Japanese medaka (Oryzias latipes) were exposed to concentrations of 0.01, 0.10, and 1.0 microg/L of the pesticide endosulfan for 24h beginning either 4-6h postfertilization or 4-6h posthatch to determine effects on hatching time, growth, mobility, foraging ability, and reproduction. Eggs exposed to endosulfan took longer to hatch, and the resulting fry were smaller at 1 week of age and had decreased mobility at 2 weeks of age. Upon reaching sexual maturity, these individuals also produced fewer eggs, and these eggs took significantly longer to hatch. Medaka exposed to endosulfan shortly after hatching did not differ in early mobility or foraging ability. Interestingly, upon reaching sexual maturity, these individuals produced more eggs than did unexposed females. The observed effects were not dose-dependent, with medaka exposed to intermediate concentrations of endosulfan (0.10 microg/L) exhibiting the greatest response. These results suggest that short-term exposure to environmentally relevant concentrations of a common pesticide may have long-term effects on growth, behavior, and reproduction in fish.

Pair Bonds and Factors Influencing the Diversity of Mating Systems in Brown-Headed Cowbirds

Observations of radio-tagged Brown-headed Cowbirds (Molothrus ater) indicated that individual males and females engage in extended associations through the breeding season. Persistent courtship by males directed at particular females and extended time spent together by certain males and females suggests that cowbirds form pair bonds. When individuals of the pair are together, females are more likely to initiate departures than males, and males are more likely to follow their mates after they depart. These observations suggest that pair bonds are being maintained by males. There were four cases of monogamy, as well as two bigamous and at least one trigamous relationship in the local population. Radio-tracking data showed that the range of a male encompassed most or all of that of his mate(s). The mating system of this population is compared with those of other populations in an attempt to assess factors influencing the diversity of cowbird mating systems. We suggest that cowbird mating systems may be influenced by both the sex ratio of the population as well as the habitat in which populations are found.

The Role of Submerged Aquatic Vegetation in Structuring the Nearshore Fish Community Within an Estuary of the Southern Gulf of St. Lawrence

Artificial fertilizers are contributing to the replacement of eelgrass (Zostera marina) by sea lettuce (Ulva lactuca) in estuaries of Prince Edward Island (PEI), Canada. In this study, we found that the nearshore fish community differed between areas dominated by these two vegetations within an estuary in every month sampled (April–August). Adult northern pipefish (Syngnathus fuscus), threespine stickleback (Gasterosteus aculeatus), blackspotted stickleback (Gasterosteus wheatlandi), and Atlantic silverside (Menidia menidia) were most strongly associated with eelgrass, while mummichog (Fundulus heteroclitus), ninespine stickleback (Pungitius pungitius), and American eel (Anguilla rostrata) were often more numerous in sea lettuce. Sea lettuce stations tended to have more young-of-the-year mummichog, fourspine stickleback (Apeltes quadracus), and Gasterosteus sp. than eelgrass stations but fewer young-of-the-year northern pipefish and Atlantic silverside. Fish richness and abundance were significantly lower in the sea lettuce than eelgrass habitat during August when benthic hypoxia occurred. We conclude that the loss of eelgrass from PEI estuaries will result in significant declines in fish biodiversity.

Effects of Acrobat MZ® and Tattoo C® on Japanese medaka (Oryzias latipes) development and adult male behavior

Exposure of Japanese medaka (Oryzias latipes) embryos and adult males to sublethal concentrations of two commonly used fungicides, Acrobat MZ and Tattoo C, had varying effects on development and adult male behavior. During embryolarval assays, medaka exposed to Acrobat exhibited decreased heart rates throughout embryonic development and were smaller at hatching than controls. Differences in hatching size were not apparent with Tattoo although some decrease in heart rate was observed at higher concentrations. Tail lesions and abnormal spinal development was a problem common to embryos exposed to Acrobat. Neither time to hatch nor early growth was affected by exposure to either fungicide. Adult males that had been exposed to high concentrations of Acrobat or Tattoo over a 28-day period were less likely to approach females during behavioral trials. The absence of other behavioral effects, particularly those related to reproductive performance, may have been due to females being sexually unreceptive during behavioral trials. No other behavioral modifications were apparent for adult males exposed to either fungicide. Information about developmental and behavioral responses to sublethal concentrations of pesticides is important for establishing environmental guidelines concerning their use.

Early Life-History Parameters of Japanese Medaka (Oryzias latipes)

Abstract The cause of size differences among developing fish is often not clear. We examined variability in egg size and in incubation time to determine whether either influenced hatching size or initial rates of growth in Japanese Medaka (Oryzias latipes). We also tested the prediction that larger females should produce heavier and/or more eggs. Our results indicated that larger females produce more, but not larger, eggs. Both egg volume and incubation time were positively, although weakly, correlated with the size of fry at hatching. Within-female variation accounted for substantially more variation in both egg size (69.9%) and hatching lengths of fry (79.3%) than did variation among females. Variation in egg volume, hatching size, and size at three-days posthatching (in the absence of feeding) decreased, as indicated by coefficients of variation for each (11.6, 4.8, 4.4). It is unknown whether slight differences in hatching size may contribute to subsequent variation in size when fry must compete for access to food.

Differences in size, pigmentation, and fluctuating asymmetry in stressed and nonstressed northern leopard frogs (Rana pipiens)

Abstract We compared a range of anatomical features of northern leopard frogs (Rana pipiens Schreber) collected from areas where deformity rates were low (-2% in nonstressed regions) and high (-40% in the stressed region) to determine if one or more of these characters might be useful in detecting developmental stress. Deformed individuals from the stressed region were significantly lighter than normal frogs both from the same region and from nonstressed regions. Body length, head width, femur length, and forelimb length were also significantly shorter in deformed and normal individuals from the stressed region than in individuals from nonstressed regions. Despite being smaller, deformed individuals had significantly larger pigment spots. Fluctuating asymmetry in femur length, femur spot area, femur spot number, and tibio-fibula length was significantly greater in deformed frogs than in normal frogs from the stressed population and the nonstressed group. Of these characters, however, only femur spot number provided a data set suitable for fluctuating asymmetry analysis (R - L values have a normal distribution, no directional asymmetry, no size-dependent asymmetry). There were no significant differences found among the three groups for fluctuating asymmetry in forelimb length, eyespot area, lateral spot number, and lateral spot area.

Mixed sexual dimorphism in semipalmated plovers

Sexually dimorphic species generally are characterized by having one sex consistently larger, and often brighter, than the other. Semipalmated Plovers (Charadrius semipalmatus) exhibit a pattern of mixed dimorphism with females that are heavier and having longer wings than males, whereas males have longer toes and bills, and are more colorful than females. Although we found weak evidence that male and female plovers mate assortatively with respect to body size, this likely resulted from birds of certain phenotypes breeding at different times. The mixed pattern of dimorphism in Semipalmated Plovers has probably resulted from different selection pressures, ecological and sexual, operating on different characters.

Sex and egg size in great-tailed Grackles

Trivers and Willard (1973) suggested that when the variance in reproductive success of one sex is greater than that of the other, females in good condition should produce more offspring of the sex that exhibits the higher variance. This assumes that the condition of the female is reflected in the condition of the offspring and that the survival and breeding success of an individual is at least partially dependent on the condition of the individual at the end of parental care. Although Trivers and Willards model predicts different strategies for different females, it is clear that nestling quality within individual broods may vary greatly and that females may potentially influence this variability in an adaptive way. For example, sequence-related hatching trends found in Lesser Snow Geese (Chen caerulescens, Ankney 1982) and Bald Eagles (Haliaeetus leucocephalus, Bortolotti 1984) may function to provide a competitive advantage for the larger sex in both species. Mead et al. (1987) recently found that eggs from which male White-crowned Sparrows (Zonotrichia leucophrys) hatched were larger than those from which females were hatched. Since the variance in reproductive success of males in this species is probably greater than that of females and since egg size has been shown in many studies to be correlated with nestling growth and survival, they interpreted these results as being an

Evaluating cumulative effects of anthropogenic inputs in Prince Edward Island estuaries using the mummichog (Fundulus heteroclitus)

Estuarine eutrophication as a result of agricultural land use, including the use of chemical fertilizers, is increasing worldwide. Prince Edward Island (PEI), Canada has very high agricultural intensity by international standards with approximately 44% of the land area under production, and some watersheds in excess of 75% agricultural land-use. The type of agriculture is also intensive with primarily row crops that have high chemical fertilizer and pesticide usage. In light of these stressors, the hypothesis of this study was that mummichog (Fundulus heteroclitus) population parameters would change with point and nonpoint source pollution, and that multivariate statistics could be used to draw associations with specific stressors. Fish were sampled on a monthly basis from May through August at 7 estuaries spanning a range of land use, nutrient, and contaminant loadings. A suite of environmental variables were simplified into 3 principal components: PC1 representing agricultural land use, N loading, and plant habitat, PC2 being dominated by sediment sand and silt distribution, and PC3 largely reflecting P loading and sediment organic matter. There were significant differences in abundance of both adult and young-of-the-year mummichog, and these changes associated most strongly with PC1, the largely N-driven agricultural influences. In contrast, somatic variables such as liver and gonad size did not show strong association with the environmental quality principal component scores. The sand and silt PC2 appeared to have the opposite association with the biological data, with siltier environments correlating to older, larger, less dense populations of mummichog. Although pesticide residues were detected in estuarine sediment, there was no clear relationship between these and watershed agricultural intensity or biochemical indicators. There was, however, a strong relationship between agricultural environmental variables (PC1) and in vitro steroid production that is suggestive of a potential chemical effect. Eutrophication appeared to be a primary stressor affecting mummichog populations, as nutrient enrichment was associated with changes in habitat variables and these in turn were associated with high mummichog density. Thus, mummichog population demographics appear to have use as an indicator of adverse or worsening conditions in estuaries. We concluded that, based on the subset of environmental factors evaluated, the nonpoint-source inputs of sediments and nutrients exerted the greatest influence on mummichog populations in PEI estuaries.

Distribution and Abundance of Salmonids in Prince Edward Island Streams

Abstract The freshwater sports fishery of Prince Edward Island (PEI) revolves largely around three salmonid species—Salvelinus fontinalis (Brook Trout), Salmo salar (Atlantic Salmon), and the nonnative Oncorhynchus mykiss (Rainbow Trout). However, little is known about their current distribution and relative abundance on the Island. Of particular concern is the status of Atlantic Salmon, whose populations have declined dramatically in other parts of the Maritimes and are listed as “may be at risk” on PEI. We systematically sampled 69 streams with suitable juvenile salmonid habitat (riffle with gravel/cobble substrate), to provide baseline data concerning the population status of these three species. Brook Trout were found in all 69 streams, with a median density of 78.3 fish per 100 m2. Atlantic Salmon were found in 23 sites, at a median density of 11.6 fish per 100 m2. Rainbow Trout were found in only 19 streams, but at slightly higher densities of 16.2 fish per 100 m2. Present day distribution and abundance of all three species on the Island have been influenced by habitat modification and degradation.