The African bonytongue, Heterotis niloticus (Pisces: Osteoglossidae), is an omnivore foraging mainly on aquatic insects, microcrustacea, seeds and detritus. We examined the diet breadth and the trophic plasticity beha...The African bonytongue, Heterotis niloticus (Pisces: Osteoglossidae), is an omnivore foraging mainly on aquatic insects, microcrustacea, seeds and detritus. We examined the diet breadth and the trophic plasticity behavior of this species (1461 specimens) in the S? River and Lake Hlan water system located in the southern Benin (West Africa). Overall, the mean diet breadths of the two populations of Heterotis from both habitats were not significantly (p ≥ 0.05) different and were not associated with seasons. However, in Lake Hlan, mean diet breadths tended to increase with size (r = 0.81) and gut length (r = 0.82) indicating that bonytongues ingest a broader range of food resources as they grow. In both habitats, the positive correlation of both standard length (Log SL) and gut length (Log GL) with the volumetric proportions of detritus and with the volumetric proportions of seeds suggests that the consumption of these two food resources increased with the size of Heterotis and with the development of the digestive tract. Likewise, the negative correlation of both (Log SL) and (Log GL) with the volumetric proportions of aquatic insects and with the volumetric proportions of microcrustacea suggests that the consumption of these two food categories decreased as the size and the gut length of Heterotis increased. The differences in the consumption of microcrustacea (13.77% in Lake Hlan versus 2.63% in S? River) and mollusks (0.73% in Lake Hlan versus 4.91% in S? River) evidenced that Heterotis shifts his trophic structure according to resource availlability in the habitat. This foraging behavior suggests a degree of trophic plasticity in Heterotis. The specialized morphological structure of Heterotis, mainly the presence of a relatively high number of gill rakers (42 - 94 rakers on the first branchial arch) during its whole life, allowing sieving of zooplankton and other microcrustacea, and the presence of the gizzard favored this trophic plasticity. The broader diet breadth coupled with the trophic plasticity behavior is probably an advantage because it enables Heterotis not only to colonize and to adapt to unstable and changing aquatic habitats, but also to invade and to well-establish in various ecosystems, such as freshwater lakes, swamps, inundated plains, streams, rivers and fish farming ponds. As a result, the wider diet breadths and the trophic plasticity behavior depicted are useful eco-ethological tool for the conservation and the aquaculture development of H. niloticus.展开更多
Optimal oviposition theory predicts a positive relationship between female pref- erence for oviposition hosts and offspring performance. Interspecies effects on oviposition preference have been widely investigated, es...Optimal oviposition theory predicts a positive relationship between female pref- erence for oviposition hosts and offspring performance. Interspecies effects on oviposition preference have been widely investigated, especially for herbivores. However, intraspecies variation, such as nitrogen content, might also influence female preference for oviposition hosts and subsequent offspring performance. To evaluate this possibility, we investigated the oviposition preference of a zoophytophagous omnivore and the development and sur- vival of its nymphs on a single species of host plant that varied in nitrogen content. In choice and no-choice experiments without prey, female omnivores were allowed to oviposit on plants that had been fertilized using 4 rates of nitrogen fertilizer （39, 78, 156, and 311 mg/L nitrogen） for 72 h. After 72 h, the most females were found on tomato plants receiving high concentrations of nitrogen fertilizer and more eggs were laid on those plants. First instar nymphs developed more rapidly on high-nitrogen plants and third instar nymphs developed faster on low-nitrogen plants. Plant nitrogen did not affect nymph survival to the adult stage, or the probability of survival over time. Although female omnivores did discriminate between potential oviposition hosts based on plant nitrogen, their choices did not significantly impact nymph development or survival. This is the first study to show that intraspecies variation in nitrogen content between plants affects the oviposition preference of female omnivores, but not offspring performance.展开更多
Objective: To investigate the diets of the Lutke’s halfbeak, Hemiramphus lutkei (H. lutkei) to determine the food and feeding habits. Methods:Samples of H. lutkei were collected from the landing sites of Karachi Coas...Objective: To investigate the diets of the Lutke’s halfbeak, Hemiramphus lutkei (H. lutkei) to determine the food and feeding habits. Methods:Samples of H. lutkei were collected from the landing sites of Karachi Coast, Pakistan. Total length was measured to the nearest 0.01 cm using digital slide calipers, and total body weight was measured using an electronic balance with 0.01 g accuracy. The dietary composition was determined from gut content examination and analysis was done using frequency of occurrence and numerical methods. To assess the changes in diet with size, H. lutkei were divided into two size groups, Group 1:14-20 cm (n=250) and Group 2:21-25 cm (n=160). Results:The total length and body weight of the sampled specimens ranged from 14 to 25 cm and 10 to 23.5 g, respectively. Out of the studied specimens, 45.12%fish stomachs were found to be empty. Dietary composition revealed daphnia, small fish, isopods, unidentified animal materials, ostracods and unidentified plant materials in the gut contents of Lutke’s halfbeak. Therefore, H. lutkei is omnivore fish feeding on algae, zooplankton, small fishes and different food items of both plant and animal origin. According to the Schoener overlap index (C), there was no significant difference in feeding of the two length groups of H. lutkei (C=0.833). On the other hand, the Shannon-Wiener index showed that the prey diversity of the Lutke's halfbeak in Group 1 was lower (H'=1.545) than that of Group 2 (H'=1.653). Conclusions:This study reports the first description of diets for H. lutkei, which would be useful for the sustainable management of this fishery in the coast of Pakistan and also neighboring countries.展开更多
文摘The African bonytongue, Heterotis niloticus (Pisces: Osteoglossidae), is an omnivore foraging mainly on aquatic insects, microcrustacea, seeds and detritus. We examined the diet breadth and the trophic plasticity behavior of this species (1461 specimens) in the S? River and Lake Hlan water system located in the southern Benin (West Africa). Overall, the mean diet breadths of the two populations of Heterotis from both habitats were not significantly (p ≥ 0.05) different and were not associated with seasons. However, in Lake Hlan, mean diet breadths tended to increase with size (r = 0.81) and gut length (r = 0.82) indicating that bonytongues ingest a broader range of food resources as they grow. In both habitats, the positive correlation of both standard length (Log SL) and gut length (Log GL) with the volumetric proportions of detritus and with the volumetric proportions of seeds suggests that the consumption of these two food resources increased with the size of Heterotis and with the development of the digestive tract. Likewise, the negative correlation of both (Log SL) and (Log GL) with the volumetric proportions of aquatic insects and with the volumetric proportions of microcrustacea suggests that the consumption of these two food categories decreased as the size and the gut length of Heterotis increased. The differences in the consumption of microcrustacea (13.77% in Lake Hlan versus 2.63% in S? River) and mollusks (0.73% in Lake Hlan versus 4.91% in S? River) evidenced that Heterotis shifts his trophic structure according to resource availlability in the habitat. This foraging behavior suggests a degree of trophic plasticity in Heterotis. The specialized morphological structure of Heterotis, mainly the presence of a relatively high number of gill rakers (42 - 94 rakers on the first branchial arch) during its whole life, allowing sieving of zooplankton and other microcrustacea, and the presence of the gizzard favored this trophic plasticity. The broader diet breadth coupled with the trophic plasticity behavior is probably an advantage because it enables Heterotis not only to colonize and to adapt to unstable and changing aquatic habitats, but also to invade and to well-establish in various ecosystems, such as freshwater lakes, swamps, inundated plains, streams, rivers and fish farming ponds. As a result, the wider diet breadths and the trophic plasticity behavior depicted are useful eco-ethological tool for the conservation and the aquaculture development of H. niloticus.
文摘Optimal oviposition theory predicts a positive relationship between female pref- erence for oviposition hosts and offspring performance. Interspecies effects on oviposition preference have been widely investigated, especially for herbivores. However, intraspecies variation, such as nitrogen content, might also influence female preference for oviposition hosts and subsequent offspring performance. To evaluate this possibility, we investigated the oviposition preference of a zoophytophagous omnivore and the development and sur- vival of its nymphs on a single species of host plant that varied in nitrogen content. In choice and no-choice experiments without prey, female omnivores were allowed to oviposit on plants that had been fertilized using 4 rates of nitrogen fertilizer （39, 78, 156, and 311 mg/L nitrogen） for 72 h. After 72 h, the most females were found on tomato plants receiving high concentrations of nitrogen fertilizer and more eggs were laid on those plants. First instar nymphs developed more rapidly on high-nitrogen plants and third instar nymphs developed faster on low-nitrogen plants. Plant nitrogen did not affect nymph survival to the adult stage, or the probability of survival over time. Although female omnivores did discriminate between potential oviposition hosts based on plant nitrogen, their choices did not significantly impact nymph development or survival. This is the first study to show that intraspecies variation in nitrogen content between plants affects the oviposition preference of female omnivores, but not offspring performance.
基金supported by the University of Karachi,Karachi,Pakistan.
文摘Objective: To investigate the diets of the Lutke’s halfbeak, Hemiramphus lutkei (H. lutkei) to determine the food and feeding habits. Methods:Samples of H. lutkei were collected from the landing sites of Karachi Coast, Pakistan. Total length was measured to the nearest 0.01 cm using digital slide calipers, and total body weight was measured using an electronic balance with 0.01 g accuracy. The dietary composition was determined from gut content examination and analysis was done using frequency of occurrence and numerical methods. To assess the changes in diet with size, H. lutkei were divided into two size groups, Group 1:14-20 cm (n=250) and Group 2:21-25 cm (n=160). Results:The total length and body weight of the sampled specimens ranged from 14 to 25 cm and 10 to 23.5 g, respectively. Out of the studied specimens, 45.12%fish stomachs were found to be empty. Dietary composition revealed daphnia, small fish, isopods, unidentified animal materials, ostracods and unidentified plant materials in the gut contents of Lutke’s halfbeak. Therefore, H. lutkei is omnivore fish feeding on algae, zooplankton, small fishes and different food items of both plant and animal origin. According to the Schoener overlap index (C), there was no significant difference in feeding of the two length groups of H. lutkei (C=0.833). On the other hand, the Shannon-Wiener index showed that the prey diversity of the Lutke's halfbeak in Group 1 was lower (H'=1.545) than that of Group 2 (H'=1.653). Conclusions:This study reports the first description of diets for H. lutkei, which would be useful for the sustainable management of this fishery in the coast of Pakistan and also neighboring countries.
