Canadian Journal of Zoology, Ahead of Print.
Many species of anurans display special mechanical abilities, such as excavation and climbing. The aim of this study is to investigate the development of traits that are associated with these special mechanical abilities, under the hypothesis that these structures attain their configuration during the juvenile stages of development. We examined specimens from four different species of Leptodactylidae and six species of Hylidae. For the digging behavior, we evaluated the progress of calcification in the anterior region of the skulls, as well as the development of the snout-ridge. To assess climbing ability, we examined the ossification rate, the variation in the shape of the phalanx, the progress of the offset angle, and the distance between the terminal phalanx and the penultimate phalange of finger IV. The ossification of the skull and phalanges, along with the development of the snout-ridge, progresses and reaches completion during the juvenile phase of ontogeny, suggesting that at the time of metamorphosis, individuals are not yet full-scale replicas of the adults. The shape and the mechanical characteristics of terminal phalanges are already established by the conclusion of metamorphosis, revealing intriguing distinctions among arboreal species with walking and jumping locomotion.
Category Archives: NRC Research Press: Canadian Journal of Zoology
Experimental manipulation of perceived predation risk alters survival, cause of death, and demographic patterns in juvenile snowshoe hares
Canadian Journal of Zoology, Ahead of Print.
Perceived predation risk alters prey behaviour and physiology, but few studies have examined downstream consequences on prey demography in wild populations. Perceived predation risk could alter adult reproductive performance via reduced investment in offspring quality and post-birth care. We manipulated perceived predation risk in snowshoe hare (Lepus americanus Erxleben, 1777) by exposing pregnant mothers to chases by a domestic dog (Canis familiaris Linnaeus, 1758). Litter size was comparable between risk-augmented and control groups, but treated females had more stillbirths and gave birth to leverets of lower body condition. Leverets from risk-augmented females had 88% higher 40-day mortality rate. Maternally preventable causes of death like starvation or predation by red squirrel (Tamiasciurus hudsonicus (Erxleben, 1777)) caused this difference, particularly during the nursing period. Risk-augmented mothers were always more active than controls, but the difference was greatest during the nursing period. We found that perceived predation risk reduces maternal productivity pre- and post-partum, implying downstream consequences to populations. Because our treatment ended before parturition, we can link offspring performance such as survival and behaviour specifically to maternal life-history trade-offs, which has not been shown in a wild mammal.
Perceived predation risk alters prey behaviour and physiology, but few studies have examined downstream consequences on prey demography in wild populations. Perceived predation risk could alter adult reproductive performance via reduced investment in offspring quality and post-birth care. We manipulated perceived predation risk in snowshoe hare (Lepus americanus Erxleben, 1777) by exposing pregnant mothers to chases by a domestic dog (Canis familiaris Linnaeus, 1758). Litter size was comparable between risk-augmented and control groups, but treated females had more stillbirths and gave birth to leverets of lower body condition. Leverets from risk-augmented females had 88% higher 40-day mortality rate. Maternally preventable causes of death like starvation or predation by red squirrel (Tamiasciurus hudsonicus (Erxleben, 1777)) caused this difference, particularly during the nursing period. Risk-augmented mothers were always more active than controls, but the difference was greatest during the nursing period. We found that perceived predation risk reduces maternal productivity pre- and post-partum, implying downstream consequences to populations. Because our treatment ended before parturition, we can link offspring performance such as survival and behaviour specifically to maternal life-history trade-offs, which has not been shown in a wild mammal.
Taxonomic revision of the sexually dimorphic flies of the Neotropical genus Euepalpus Townsend, 1908 (Diptera: Tachinidae), with notes on sexual patches in Tachinini
Canadian Journal of Zoology, Ahead of Print.
Euepalpus Townsend, 1908 is a small Neotropical genus of bristle flies (Diptera: Tachinidae: Tachinini), which includes two valid species whose taxonomy is unclear, mainly because males and females are sexually dimorphic. Males exhibit a pair of sexual patches on the dorsal surface of abdominal tergite 5, an unusual feature in Tachinidae. Here, the genus is revised, including a key to species and detailed descriptions and illustrations of the type material and males and females of each species. The male and female terminalia of Euepalpus species are described for the first time. Finally, I discuss the occurrence and distribution of sexual patches in Tachinini.
Euepalpus Townsend, 1908 is a small Neotropical genus of bristle flies (Diptera: Tachinidae: Tachinini), which includes two valid species whose taxonomy is unclear, mainly because males and females are sexually dimorphic. Males exhibit a pair of sexual patches on the dorsal surface of abdominal tergite 5, an unusual feature in Tachinidae. Here, the genus is revised, including a key to species and detailed descriptions and illustrations of the type material and males and females of each species. The male and female terminalia of Euepalpus species are described for the first time. Finally, I discuss the occurrence and distribution of sexual patches in Tachinini.
Microhabitat use of northern and southern flying squirrels in a recent hybrid zone
Canadian Journal of Zoology, Ahead of Print.
Secondary contact of closely related species may lead to hybridization if reproductive isolation is incomplete. We examined the role of habitat use as a factor contributing to reproductive isolation of northern (Glaucomys sabrinus (Shaw, 1801)) and southern (Glaucomys volans (Linnaeus, 1758)) flying squirrels in an area of secondary contact in Ontario, Canada. Specifically, we looked at summer microhabitat use within sites of sympatry and allopatry to test for evidence of reinforcement due to diverging habitat use. We also examined differences in broad-scale habitat features at woodlots to determine predictors of species occurrence across sites. We used 18 years (2002–2019) of flying squirrel summer capture data from six sites along a north–south transect and microhabitat data from vegetation surveys conducted during summer 2016. We found microhabitat variables to be weak predictors of trap-level flying squirrel presence, and we found no evidence of divergence in microhabitat use over the 18 years. Further, we found latitude, not broad-scale habitat, was the strongest predictor of site-level flying squirrel occurrence. Overall, our findings suggest that microhabitat-based isolation is not being reinforced between flying squirrels; however, hybridization may be limited to areas where climate and habitat are suitable for both species.
Secondary contact of closely related species may lead to hybridization if reproductive isolation is incomplete. We examined the role of habitat use as a factor contributing to reproductive isolation of northern (Glaucomys sabrinus (Shaw, 1801)) and southern (Glaucomys volans (Linnaeus, 1758)) flying squirrels in an area of secondary contact in Ontario, Canada. Specifically, we looked at summer microhabitat use within sites of sympatry and allopatry to test for evidence of reinforcement due to diverging habitat use. We also examined differences in broad-scale habitat features at woodlots to determine predictors of species occurrence across sites. We used 18 years (2002–2019) of flying squirrel summer capture data from six sites along a north–south transect and microhabitat data from vegetation surveys conducted during summer 2016. We found microhabitat variables to be weak predictors of trap-level flying squirrel presence, and we found no evidence of divergence in microhabitat use over the 18 years. Further, we found latitude, not broad-scale habitat, was the strongest predictor of site-level flying squirrel occurrence. Overall, our findings suggest that microhabitat-based isolation is not being reinforced between flying squirrels; however, hybridization may be limited to areas where climate and habitat are suitable for both species.
Running overnight and struggling to find sea ice: long-distance movement by an Arctic fox (Vulpes lagopus) from Russia
Canadian Journal of Zoology, Ahead of Print.
Given the scale, speed, and complexity of recent changes in the Arctic, our understanding of their multiple implications for Arctic biota is still limited. We detail for the first time in the vast Russian Arctic the long-distance movement of an Arctic fox (Vulpes lagopus (Linnaeus, 1758)) tracked with a GPS/iridium collar providing considerably high precision (several meters) and frequency of locations (every 4 h). Revealed diurnal activity patterns of the Arctic fox indicate that it ran greater distances in night hours and shortest in day hours during the most intense movement period. The movement records suggested several attempts to leave the land, as it seemed to encounter open water four times on different parts of Yamal peninsula. The Arctic fox crossed the Ob Bay towards the Gydan peninsula and satellite imagery of discontinuous ice during crossing suggested that it might have stayed on pieces of floating ice. Our observation may support evidence that a reduction in the duration and extent of sea ice could affect the ability of Arctic foxes to cover long distances and thus, in the long term, the connectivity between populations. Similar studies are needed aiming to understand movement ecology of the Arctic foxes in the changing Arctic.
Given the scale, speed, and complexity of recent changes in the Arctic, our understanding of their multiple implications for Arctic biota is still limited. We detail for the first time in the vast Russian Arctic the long-distance movement of an Arctic fox (Vulpes lagopus (Linnaeus, 1758)) tracked with a GPS/iridium collar providing considerably high precision (several meters) and frequency of locations (every 4 h). Revealed diurnal activity patterns of the Arctic fox indicate that it ran greater distances in night hours and shortest in day hours during the most intense movement period. The movement records suggested several attempts to leave the land, as it seemed to encounter open water four times on different parts of Yamal peninsula. The Arctic fox crossed the Ob Bay towards the Gydan peninsula and satellite imagery of discontinuous ice during crossing suggested that it might have stayed on pieces of floating ice. Our observation may support evidence that a reduction in the duration and extent of sea ice could affect the ability of Arctic foxes to cover long distances and thus, in the long term, the connectivity between populations. Similar studies are needed aiming to understand movement ecology of the Arctic foxes in the changing Arctic.
Standard metabolic rate differs between rainbow trout (Oncorhynchus mykiss) growth forms
Canadian Journal of Zoology, Ahead of Print.
In variable environments, repeatable phenotypic differences between individuals provide the variation required for natural selection. The pace-of-life syndrome (POLS) provides a conceptual framework linking individual physiology and life histories to behaviour, where rapidly growing individuals demonstrate higher rates of resting or “standard” metabolic rate (SMR). If differences in SMR are consistent between fast- and slow-growing individuals, these differences may be important to capture in bioenergetic relationships used to describe their growth, energy acquisition, and allocation. We compared growth rates and SMR between a domesticated and wild strain of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) using intermittent flow respirometry. Though mass-scaling exponents were similar between strains, mass-scaling coefficients of SMR for fast-growing rainbow trout were 1.25 times higher than those for slower growing fish. These observed differences in mass-scaling coefficients between fast- and slow-growing rainbow trout were consistent with data extracted from several other studies. Bioenergetic estimates of consumption for domestic strain fish increased as the difference in SMR and wild strain fish increased, and increased as activity level increased. Our results indicate patterns of SMR consistent with POLS, and suggest that strain-specific SMR equations may be important for applications to active populations (i.e., field observations).
In variable environments, repeatable phenotypic differences between individuals provide the variation required for natural selection. The pace-of-life syndrome (POLS) provides a conceptual framework linking individual physiology and life histories to behaviour, where rapidly growing individuals demonstrate higher rates of resting or “standard” metabolic rate (SMR). If differences in SMR are consistent between fast- and slow-growing individuals, these differences may be important to capture in bioenergetic relationships used to describe their growth, energy acquisition, and allocation. We compared growth rates and SMR between a domesticated and wild strain of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) using intermittent flow respirometry. Though mass-scaling exponents were similar between strains, mass-scaling coefficients of SMR for fast-growing rainbow trout were 1.25 times higher than those for slower growing fish. These observed differences in mass-scaling coefficients between fast- and slow-growing rainbow trout were consistent with data extracted from several other studies. Bioenergetic estimates of consumption for domestic strain fish increased as the difference in SMR and wild strain fish increased, and increased as activity level increased. Our results indicate patterns of SMR consistent with POLS, and suggest that strain-specific SMR equations may be important for applications to active populations (i.e., field observations).
Environmental drivers of juvenile dispersal and adult non-breeding movements in Ambystoma salamanders
Canadian Journal of Zoology, Ahead of Print.
Understanding the environmental drivers of species’ dispersal and migration patterns is needed to accurately predict climate change impacts on populations. For pond-breeding amphibians, adult movements associated with the breeding period are well studied but major gaps exist in our knowledge of the drivers of adult and juvenile non-breeding movements. Here, we assess environmental drivers of adult and juvenile Ambystoma maculatum (Shaw, 1802), Ambystoma jeffersonianum (Green, 1827), and their unisexual dependants’ (Ambystoma laterale–jeffersonianum (Uzzell, 1964)) summer and fall non-breeding movements using data from pitfall trapping and radio telemetry tracking. We used generalized linear models to assess the influence of precipitation, minimum temperature, day of year, and days since last precipitation on salamander movements. Juvenile summer dispersal movements were related to days since last precipitation in Jefferson Salamander complex individuals and 24 h precipitation in Spotted Salamanders. Adult and juvenile fall movements were driven by minimum temperature, 24 h precipitation, and days since last precipitation, and the effect of these environmental factors varied slightly between species and between Jefferson bisexuals and unisexuals. Our work indicates that changes in both temperature and precipitation will likely impact non-breeding dispersal and migration in these species and, overall, improves our understanding of ecological patterns throughout their entire life cycle.
Understanding the environmental drivers of species’ dispersal and migration patterns is needed to accurately predict climate change impacts on populations. For pond-breeding amphibians, adult movements associated with the breeding period are well studied but major gaps exist in our knowledge of the drivers of adult and juvenile non-breeding movements. Here, we assess environmental drivers of adult and juvenile Ambystoma maculatum (Shaw, 1802), Ambystoma jeffersonianum (Green, 1827), and their unisexual dependants’ (Ambystoma laterale–jeffersonianum (Uzzell, 1964)) summer and fall non-breeding movements using data from pitfall trapping and radio telemetry tracking. We used generalized linear models to assess the influence of precipitation, minimum temperature, day of year, and days since last precipitation on salamander movements. Juvenile summer dispersal movements were related to days since last precipitation in Jefferson Salamander complex individuals and 24 h precipitation in Spotted Salamanders. Adult and juvenile fall movements were driven by minimum temperature, 24 h precipitation, and days since last precipitation, and the effect of these environmental factors varied slightly between species and between Jefferson bisexuals and unisexuals. Our work indicates that changes in both temperature and precipitation will likely impact non-breeding dispersal and migration in these species and, overall, improves our understanding of ecological patterns throughout their entire life cycle.
Differential digestive and metabolic profile of juveniles and adults of the estuarine-dependent marine fish Mugil liza (Mugilidae) cohabiting inside a southwestern Atlantic coastal lagoon
Canadian Journal of Zoology, Ahead of Print.
Integrative studies on intraspecific differences of digestive enzymes, energy reserves, and morphological/somatic traits in juveniles and adults of estuarine-dependent marine fish while inhabiting inside a coastal lagoon are lacking. This study was carried on juveniles and adults of Mugil liza Valenciennes, 1836 inhabiting inside Mar Chiquita Coastal Lagoon (Argentina). Both stages exhibited amylase, maltase, sucrase, lipase, trypsin, and aminopeptidase-N activities in the intestine, which were active over a wide range of pH and temperatures and exhibited Michaelis–Menten kinetics. Adults exhibited higher intestinal coefficient (31%), higher amylase (32%), and lower maltase (82%) and lipase activities (38%). Glycogen concentration in liver and muscle was similar, while free glucose concentration was higher in adults (772% and 400%, respectively). In adults, retroperitoneal fat (absent in juveniles) constituted the main triglycerides (TAG) storage site, while TAG concentration in liver and muscle was lower (86% and 80%, respectively) than that in juveniles. No differences were found in protein concentration in any storage organ. The results show that juveniles and adults exhibit a digestive and metabolic profile at the biochemical level and intraspecific differences in key components of carbohydrate and lipid metabolism that could support preparation for reproductive migration of adults outside the coastal lagoon.
Integrative studies on intraspecific differences of digestive enzymes, energy reserves, and morphological/somatic traits in juveniles and adults of estuarine-dependent marine fish while inhabiting inside a coastal lagoon are lacking. This study was carried on juveniles and adults of Mugil liza Valenciennes, 1836 inhabiting inside Mar Chiquita Coastal Lagoon (Argentina). Both stages exhibited amylase, maltase, sucrase, lipase, trypsin, and aminopeptidase-N activities in the intestine, which were active over a wide range of pH and temperatures and exhibited Michaelis–Menten kinetics. Adults exhibited higher intestinal coefficient (31%), higher amylase (32%), and lower maltase (82%) and lipase activities (38%). Glycogen concentration in liver and muscle was similar, while free glucose concentration was higher in adults (772% and 400%, respectively). In adults, retroperitoneal fat (absent in juveniles) constituted the main triglycerides (TAG) storage site, while TAG concentration in liver and muscle was lower (86% and 80%, respectively) than that in juveniles. No differences were found in protein concentration in any storage organ. The results show that juveniles and adults exhibit a digestive and metabolic profile at the biochemical level and intraspecific differences in key components of carbohydrate and lipid metabolism that could support preparation for reproductive migration of adults outside the coastal lagoon.
Regulation of feed intake, digestive enzyme activity, and growth in response to live feed and prepared diet during early rearing of Labeo rohita
Canadian Journal of Zoology, Ahead of Print.
A 35 day feeding trial in a replicate of five was conducted to evaluate the impact of partial and total replacement of live feed (LF) with nanoparticulate-prepared diet (ND) on early rearing of rohu (Labeo rohita (Hamilton, 1822)). Larvae 3 days after hatching (DAH) were evenly distributed into three groups; T1 was reared exclusively on LF, T2 was on ND, and T3 was co-fed both LF and ND (1:1). All groups showed a feed-dependent increase in growth and the expression of genes involved in feed intake and growth with age DAH. The T3 group showed significantly higher weight gain, specific growth rate, and expression of insulin-like growth factor-1 followed by the T2 group, while the highest expression of ghrelin and growth hormone secretagogue receptor was observed in T3 followed by T1. Furthermore, leptin showed the highest expression in the T2 followed by the T1 group. The intestinal enzymes showed variable trends, with the highest activity of cellulase, amylase, and protease in the T1, T2, and T3 groups, respectively. Moreover, in all groups, cellulase increased continuously with age DAH, while amylase and protease showed a positive correlation up to 30 DAH and then declined. The results of this study could be helpful in larval nutrition programming.
A 35 day feeding trial in a replicate of five was conducted to evaluate the impact of partial and total replacement of live feed (LF) with nanoparticulate-prepared diet (ND) on early rearing of rohu (Labeo rohita (Hamilton, 1822)). Larvae 3 days after hatching (DAH) were evenly distributed into three groups; T1 was reared exclusively on LF, T2 was on ND, and T3 was co-fed both LF and ND (1:1). All groups showed a feed-dependent increase in growth and the expression of genes involved in feed intake and growth with age DAH. The T3 group showed significantly higher weight gain, specific growth rate, and expression of insulin-like growth factor-1 followed by the T2 group, while the highest expression of ghrelin and growth hormone secretagogue receptor was observed in T3 followed by T1. Furthermore, leptin showed the highest expression in the T2 followed by the T1 group. The intestinal enzymes showed variable trends, with the highest activity of cellulase, amylase, and protease in the T1, T2, and T3 groups, respectively. Moreover, in all groups, cellulase increased continuously with age DAH, while amylase and protease showed a positive correlation up to 30 DAH and then declined. The results of this study could be helpful in larval nutrition programming.
Differences in thermal energetics of the cave myotis (Myotis velifer) from a cool and a warm environment of central Mexico
Canadian Journal of Zoology, Ahead of Print.
Endotherm homeotherms deal with the energetic cost of maintaining a stable body temperature (Tb) in ecosystems differing in ambient temperature (Ta). In response, animals adjust some of their thermal energetics to meet the energy requirements of thermoregulation. Bats are small mammals with a geographical distribution that may include environments with different Ta. Therefore, these animals should adjust their thermal energetics depending on the environmental characteristics of the habitats where they live. Using open-flow respirometry, we measured basal metabolic rate (BMR), thermal conductance (C’), lower and upper critical temperatures (TLC and TUC), and breadth of the thermoneutral zone (TNZb) of the cave myotis (Myotis velifer (J.A. Allen, 1890)) living in a coniferous forest versus a tropical deciduous forest in central Mexico. To our knowledge, this is the first attempt to measure thermal energetics at the intraspecific level in populations measured at the same time. Bats from the coniferous forest had lower BMR, C’, TLC, TUC, and a wider TNZb than bats from the tropical deciduous forest. The results we found here are likely the consequence of the differences between the energy demands imposed by Ta, where the animals roost, and the Ta and prey availability of their foraging areas. These differences may help individuals regulate their heat production and dissipation to maintain low thermoregulatory costs in the places they inhabit.
Endotherm homeotherms deal with the energetic cost of maintaining a stable body temperature (Tb) in ecosystems differing in ambient temperature (Ta). In response, animals adjust some of their thermal energetics to meet the energy requirements of thermoregulation. Bats are small mammals with a geographical distribution that may include environments with different Ta. Therefore, these animals should adjust their thermal energetics depending on the environmental characteristics of the habitats where they live. Using open-flow respirometry, we measured basal metabolic rate (BMR), thermal conductance (C’), lower and upper critical temperatures (TLC and TUC), and breadth of the thermoneutral zone (TNZb) of the cave myotis (Myotis velifer (J.A. Allen, 1890)) living in a coniferous forest versus a tropical deciduous forest in central Mexico. To our knowledge, this is the first attempt to measure thermal energetics at the intraspecific level in populations measured at the same time. Bats from the coniferous forest had lower BMR, C’, TLC, TUC, and a wider TNZb than bats from the tropical deciduous forest. The results we found here are likely the consequence of the differences between the energy demands imposed by Ta, where the animals roost, and the Ta and prey availability of their foraging areas. These differences may help individuals regulate their heat production and dissipation to maintain low thermoregulatory costs in the places they inhabit.