Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among ...lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential ω-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene
in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of
in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in
copies, indicating its key role in freshwater colonization.
The Mekong giant catfish
Pangasianodon gigas
is endemic to the Mekong River and is one of the largest freshwater fish. This critically endangered species is a popular food for local people and a ...commercially essential fishery resource. Ecological knowledge of this catfish is required to conserve it. However, its ecology has not yet been well studied. We monitored the food intake of the Mekong giant catfish in a stable aquarium for over 13 years. We analyzed their feeding rhythms and fasting periods. The feeding rhythm (circannual rhythm) of the Mekong giant catfish over 13 years and its temporal variations were revealed. Four of the six catfish showed feeding cycles that extended more than one year (395.7 days). Five of the six catfish showed prolonged fasting periods over 30 consecutive days. These patterns coincide with the wet/dry seasons in Thailand, corresponding to the abundance of catfish food resources (
Cladophora
spp.). Furthermore, it is suggested that the Mekong catfish has acquired the physiological ability to tolerate a fasting state for about 1 year, possibly because this species may have survived many critical situations in the Mekong River in the past, such as food insufficiency. At the same time, however, this also indicates that the fish is highly dependent on
Cladophora
spp. as a food item and may not be able to substitute other food items. From these, reductions in food items or feeding habitats for catfish after damming in many places of the Mekong River basin may decrease the population size of this species.
Behavioral laterality-typically represented by human handedness-is widely observed among animals. However, how laterality is acquired during development remains largely unknown. Here, we examined the ...effect of behavioral experience on the acquisition of lateralized predation at different developmental stages of the scale-eating cichlid fish Perissodus microlepis. Naïve juvenile fish without previous scale-eating experience showed motivated attacks on prey goldfish and an innate attack side preference. Following short-term predation experience, naïve juveniles learned a pronounced lateralized attack using their slightly skewed mouth morphology, and improved the velocity and amplitude of body flexion to succeed in foraging scales during dominant-side attack. Naïve young fish, however, did not improve the dynamics of flexion movement, but progressively developed attack side preference and speed to approach the prey through predation experience. Thus, the cichlid learns different aspects of predation behavior at different developmental stages. In contrast, naïve adults lost the inherent laterality, and they neither developed the lateralized motions nor increased their success rate of predation, indicating that they missed appropriate learning opportunities for scale-eating skills. Therefore, we conclude that behavioral laterality of the cichlid fish requires the integration of genetic basis and behavioral experiences during early developmental stages, immediately after they start scale-eating.
Recently, anthropogenic alterations have had severe and negative impacts on the terrestrial and aquatic species and environments. To conserve species that have a small and limited habitat, it is ...necessary to focus on fine-scale population structure and its effects on persistence. The deepbodied bitterling
Acheilognathus longipinnis
is an endangered freshwater fish that occupies ponds scattered in lateral bars in the Kiso River. In this study, we conducted multi-locus microsatellite DNA analysis to evaluate both fine-scale population structure and genetic diversity, in order to conserve
A. longipinnis
. The smaller number of loci deviating from the Hardy–Weinberg equilibrium in ponds scattered in individual lateral bars compared to the whole river system suggests that
A. longipinnis
forms a local breeding population in units of ponds. The population was roughly split between the river banks and the local population located in ponds in the mid-channel bar showed intermediate relationships with the river bank populations. Gene flow between local populations was not always homogeneous and was not influenced by geographical distances between local populations or the direction of river flow. The dispersal of
A. longipinnis
across both river bank sides may be constrained and is probably affected by the ecological characteristics of
A. longipinnis
and the hydrological regimes. Consequently,
A. longipinnis
in the Kiso River is maintained as a complex of multiple local populations with appropriate gene flow among them. To conserve
A. longipinnis
, both the persistence of the unstable ponds and moderate genetic exchanges by individual migration are required.
To conserve endangered species, maintenance of both interpopulational and intrapopulational genetic diversity is often required in wild populations. For the Itasenpara bitterling (
Acheilognathus ...longipinnis
), its limited number of habitats in three areas of Japan are all threatened. In this study, microsatellite data were obtained from DNA sampled from all three wild populations to evaluate the interpopulational and intrapopulational genetic diversity of
A. longipinnis
. The genetic uniqueness of each population and genetic differentiation among populations were determined, which are probably due to both spatial and temporal isolation among populations. Both the long-term and contemporary effective population sizes (
N
e
) were estimated for all populations. In all populations, the presence of historic and recent bottlenecks was estimated. For the population from the Moo River, which has the smallest habitat area and the highest number of individuals, Bayesian skyline plots demonstrated a drastic decrease in effective population size, likely caused by anthropogenic habitat modification in the past. The population from the Kiso River demonstrated a similar trend in genetic demography to the population from the Moo River. In contrast, a gradual decline in
N
e
was observed in the population from the Yodo River, which continued until recently. The populations from the Moo and Kiso rivers are deemed to be critically endangered due to the loss of heterozygosity. Therefore, conservation efforts are needed to maintain and promote genetic diversity in each population, both through habitat conservation and captive breeding efforts.
To manage biological invasions effectively, the impacts of alien species on the demography and traits of native species must be known, but determining those impacts can be challenging. We used a ...comparative approach to gain insight into the impacts that an alien toad (Bufo japonicus formosus) might have on native Japanese predatory amphibians. We compared the susceptibility of native predator species to alien toad toxins in the alien‐invaded range and the susceptibility of closely related native predator species to the toxins in the alien toad's native range to investigate the impacts of an alien on a native species.
Bufo japonicus formosus is native to Honshu, but was recently introduced to Hokkaido and Sado. In laboratory experiments, we compared individual mortality of predators exposed to a toad hatchling between novel predators on the toad‐invaded islands and ecologically similar congeneric or conspecific species on Honshu, where the toad is native. We also compared (1) the percentage of individuals that consumed a toad hatchling and (2) toxin resistance (i.e. survival and growth of individuals after toad consumption) between these two groups of predators, as mechanistic components behind the susceptibility of the predators to the toxic prey.
The mortality of Rana pirica from all populations after consumption of a toad hatchling was almost 100%, and that of Hynobius retardatus ranged from 14 to 90%, depending on the population. In contrast, the mortality of Rana ornativentris and Hynobius nigrescens was near 0% regardless of population. These differences between congeneric predators were mostly due to differences in their toxin resistance.
These results suggest that the alien toad is a potential threat to the novel amphibian predators on Hokkaido, although they also imply that the novel predators on Hokkaido have the potential to develop toxin resistance through adaptive evolution. However, this counteradaptation may have a higher chance of evolving in H. retardatus than in R. pirica because of differences in their genetic backgrounds.
The Mekong giant catfish
is one of the largest freshwater fish, measuring up to 3 m in total length. This study was designed to determine the feeding habits of
to better understand how the fish ...achieve their large body size. We compared the relationship between gut length (GL) and total length (TL) among related species in superfamily Bagroidea, order Siluriformes (
and
) in the Kaeng Krachan reservoir, Thailand. The mean relative gut length (RGL = GL / TL) of
was 3.50, showing that they have relatively long guts, with values more similar to those of omnivorous
(RGL = 3.70) than to those of carnivorous
(RGL = 0.92). In the allometric relationship (i.e., log
GL = log
+
log
TL), the slope close to 1 for
(
= 1.07) has been widely observed in carnivores, while
has a greater intercept of the linear equation than
and
, resulting in a similar GL of
to omnivorous
at approximately 35 cm in TL. Moreover, GL of
at 150 to 250 cm in TL showed great variations (RGL = 1.35-6.32). The variation in RGL for
seemed to result from a poor nutritional state. In conclusion,
is suggested to feed on indigestible materials such as plants, algae, and sediments, and potentially experience fasting in a reservoir.
Large-bodied animals, such as the Mekong giant catfish (
Pangasianodon gigas
), may modify prey communities and affect their potential competitors for food resources by consuming large quantities of ...prey. The Mekong giant catfish is a key representative of freshwater megafauna and is stocked in reservoirs in Thailand for species conservation and fishery stock enhancement. However, their biological interactions with other sympatric animals remain unclear. Here, we aimed to investigate the trophic niche of the Mekong giant catfish in a Thai reservoir by comparing stable carbon and nitrogen isotope ratios (
δ
13
C and
δ
15
N, respectively) and fatty acid (FA) composition with those of five other sympatric fish species. The
δ
13
C value of the Mekong giant catfish was –24.4 ± 1.0‰ (mean ± SD), the second highest among the sympatric fish species, suggesting relatively weak reliance on phytoplankton-based food chains. The
δ
15
N value of the Mekong giant catfish was 10.7 ± 0.4‰, intermediate between those of herbivorous and carnivorous fishes, indicating that it is not a primary consumer. The FA composition of the Mekong giant catfish significantly differed from those of the other fish species and was characterized by a large proportion of long-chain FA, including 22:6n-3, 20:5n-3, and 20:1n-9. The
δ
13
C,
δ
15
N, and FA signatures suggest that the Mekong giant catfish occupy distinct trophic niches in food webs. Our results highlight that it is necessary to monitor the ecological impacts of released Mekong giant catfish on lower-level consumers through their foraging in receiving reservoirs.
To conserve endangered species, the maintenance of
ex situ
captive populations with sustainable genetic diversity is often required, in combination with population viability analysis (PVA). Since ...2010, the threatened Itasenpara bitterling
Acheilognathus longipinnis
lineages in the Kiso region, Japan, have been maintained in
ex situ
rearing facilities to allow for conservation efforts. In this study, we obtained microsatellite data from DNA extracted from these captive populations to elucidate their genetic diversity and effective population size. The populations of several initial generations indicated a deviation from Hardy–Weinberg equilibrium, probably due to the limited number of extracted founder individuals analyzed. The effective population size of the captive population tended to increase over the course of generations, although the degree of genetic diversity tended to decrease highlighting the concern for the progression of inbreeding. Our prediction based on the PVA suggests that the maintenance of the captive population under the current conditions could lead to extinction of the Itasenpara bitterling in 50 years. In contrast, simultaneously increasing the carrying capacity and individual exchange among populations appears to enhance the effective management of captive Itasenpara bitterling populations.
EX situ conservation management is an effective method that conserves endangered species that are on the decline owing to anthropogenic alteration of natural habitats. This entails the management of ...a captive population while maintaining its genetic variability and preventing its adaptation to the captive environment. However, implementation of such efforts is largely limited to experimental animals and zoo-managed animals with pedigree information. In this study, ex situ management of endangered Itasenpara bitterling (
Acheilognathus longipinnis
) was conducted, while practicing recommended conservation procedures, for the purpose of conserving this species. In this 11 year long study, we conducted multi-locus microsatellite DNA analyses to evaluate the genetic dynamics of an ex situ captive population of
A. longipinnis
, as well as the wild
A. longipinnis
population of the Kiso River. Genetic diversity generally varied between yearly cohorts in each of the captive sub-populations, and some showed a stable increasing trend with generations. When all sub-populations were considered as one population, genetic diversity was maintained at a high value, while effective population size generally reached target values, thereby preventing inbreeding. These results were achieved by maintaining multiple captive sub-populations and exchanging individuals between them. Simultaneously, the introduction of additional individuals from the wild population produced genetic variability in the captive population. These fluctuating patterns of genetic diversity in the captive
A. longipinnis
population were desirable compared to previously predicted values. Consequently, these findings show that the current ex situ conservation program is suitable for maintaining the genetic composition of the captive population of
A. longipinnis
.
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