Examination of the Trexler-DeAngelis Model of Maternal Provisioning Reveals That Matrotrophy Is Costly

The evolution of matrotrophy (post-fertilization maternal provisioning to developing embryos) has been explained through several hypotheses. Trexler and DeAngelis proposed in 2003 a theoretical model that defines the ecological conditions under which matrotrophy would be favored over lecithotrophy (pre-fertilization maternal provisioning). According to this model, matrotrophy offers a selective advantage in environments with abundant and constantly available food, whereas environments with limited and fluctuating food resources should instead promote a lecithotrophic mode of maternal provisioning. This model also proposes that matrotrophy entails the consequence of leaner reproductive females and in turn shorter lifespans. In this study, we examined the Trexler-DeAngelis model using data from 45 populations of five viviparous species from the fish genus Poeciliopsis (family Poeciliidae). We used the matrotrophy index (MI) as a measure of post-fertilization maternal provisioning, and the index of stomach fullness and individual body condition (BC) as proxies for food availability. We also estimated the magnitude of fluctuations in food availability by calculating the temporal variances of these two proxies. Neither abundant nor constantly available food were associated with greater degrees of matrotrophy, which fails to support the predictions of the Trexler-DeAngelis model with respect to the ecological drivers of increased post-fertilization provisioning to embryos. Nonetheless, in all five species we observed that females with greater degrees of matrotrophy had poorer BC compared to females that provided less nutrients to embryos after fertilization. This finding is consistent with one of the expected consequences of advanced matrotrophy according to the Trexler-DeAngelis model, namely, a detriment to the nutritional status of females. Our study provides compelling evidence that gestating females experience a trade-off between post-fertilization provisioning to embryos and self-maintenance, revealing in turn that matrotrophy is a costly reproductive strategy.

State of Satiation Partially Regulates the Dynamics of Vertical Migration

Vertical migrations into shallower waters at night are beneficial for migrators as they reduce predation risk and allow migrators to encounter a higher density of prey. Nevertheless, ocean acoustics data and trawl data have shown that a portion of some vertically migrating populations remain at depth and do not migrate. One hypothesis for this phenomenon is the Hunger-Satiation hypothesis, which in part states that the non-migrating portion of the migrating species-assemblage refrains from migrating if they have full or partially full stomachs from daytime or nocturnal feeding. However, stomach fullness of the non-migrating subpopulation compared to the migrating portion has rarely been studied, due to the difficulty in obtaining sufficient samples. The stomach fullness levels of numerically abundant crustacean and fish species with well-known depth distributions were quantified in the present study. Animals were captured during night trawls from discrete-depth intervals between 0 and 1,500 m. Stomach fullness indices were assigned from 0 to 5 and compared between migratory taxa caught in shallow and deep waters. Data from the crustaceansAcanthephyra purpurea, Gardinerosergia splendens, Plesionika richardi, andSystellaspsis debilis, as well as the fishesLampanyctus alatus, Lepidophanes guentheri, andNotolychnus valdiviae, provided support for the Hunger-Satiation hypothesis, while data from the crustaceansGennadas capensisandGennadas valensand the fishBenthosema suborbitaledid not. These findings suggest that stomach vacancy may be just one of several factors regulating the dynamics of vertical migration in those species whose behavioral plasticity suggests daily “choices” in whether or not to vertically migrate.

Damming in the Madeira River modifies the food spectrum of piscivorous and affects their resource partitioning

Phylogenetic proximity suggests some degree of diet similarity among species. Usually, studies of diet show that species coexistence is allowed by partitioning food resources. We evaluate how visually oriented piscivorous fishes (Characiformes) share prey before and after building the Santo Antônio Hydroelectric Power Plant (HPP) in the Madeira River (Brazil), the largest muddy-water tributary of the Amazon River. Piscivorous species (Acestrorhynchus falcirostris, Acestrorhynchus heterolepis, Hydrolycus scomberoides, and Rhaphiodon vulpinus) were sampled under pristine (pre-HPP) and disturbed (post-HPP) environmental conditions. We analyzed species abundance and stomach contents for stomach fullness and prey composition to check variations between congeneric and non-congeneric species. The percent volume of prey taxa was normalized by stomach fullness and grouped into the taxonomic family level to determine diet, niche breadth, and overlap. Only R. vulpinus abundance increased in post-HPP. There was no significant variation in niche breadth between the periods, while niche overlap decreased in congeneric and non-congeneric species. Our results indicate that river impoundment affected piscivorous fishes in distinct ways and modified their resource partitioning. Therefore, evaluate interspecific interactions is a required tool to understand how fishes respond to river damming.

Biological characteristics of the japanese scad Decapterus maruadsi in Thuan An estuary, Thua Thien Hue Province

A total of 257 Decapterus maruadsi individuals of collected from Thuan An estuary in Phu Vang District, Thua Thien Hue Province were analyzed. Results showed that the fork length ranged from 90 mm to 215 mm (160.2 mm on average) and mainly in the 140–180 mm range (86.8 %). Of three age groups (0+ to 2+), the fished stock belongfrom is primarily to the 1+ age group (63.8%) and 0+ age group (28.8%). Of five stomach fullness levels (0 to 4), the second and fourth degree made up significantly proportions, being 29.6% and 31.5%, respectively. For the five fat levels (0 to 4), the fourth degree made up 86.0%. The females to males ratio was 1.00 : 1.42. von Bertalanffy’s growth model followed the equation: Lt = 203.77 × (1–e-0.3747(t+3.0272)).

Feeding ecology of electric eel Electrophorus varii (Gymnotiformes: Gymnotidae) in the Curiaú River Basin, Eastern Amazon

ABSTRACT In this study, the composition of the diet and the feeding activity of Electrophorus varii were evaluated. The influence of ontogeny and seasonality in these feeding parameters was also examined. Fish were collected in the Curiaú River Basin, Amazon, Brazil, from March 2005 to February 2006, during the rainy (January-June) and dry (July-December) seasons. Diet composition was characterized based on the analysis of stomach contents and feeding dynamics was assessed based on the Stomach Fullness Index (IR) calculated using stomach weight. Stomach content and RI data were grouped into four-cm size classes (40-80, 80-120, 120-160, and 160-200) and two seasonal periods (rainy and dry). The influence of ontogeny and seasonality in the diet was investigated through PERMANOVA, and in the food dynamics through ANOVA. The analysis of stomach contents revealed that fish were the most consumed preys by electric eels, especially Callichthyidae and Cichlidae. Diet composition and RI values of electric eels were not influenced by ontogeny and seasonality. Electric eels are fish predators, regardless of size class and seasonal period.

Biological characteristics of the japanese scad Decapterus maruadsi in Thuan An estuary, Thua Thien Hue Province

A total of 257 Decapterus maruadsi individuals of collected from Thuan An estuary in Phu Vang District, Thua Thien Hue Province were analyzed. Results showed that the fork length ranged from 90 mm to 215 mm (160.2 mm on average) and mainly in the 140–180 mm range (86.8 %). Of three age groups (0+ to 2+), the fished stock belongfrom is primarily to the 1+ age group (63.8%) and 0+ age group (28.8%). Of five stomach fullness levels (0 to 4), the second and fourth degree made up significantly proportions, being 29.6% and 31.5%, respectively. For the five fat levels (0 to 4), the fourth degree made up 86.0%. The females to males ratio was 1.00 : 1.42. von Bertalanffy’s growth model followed the equation: Lt = 203.77 × (1–e-0.3747(t+3.0272)).

Comparison of the feeding ecology of Perisesarma eumolpe collected at the intact forest and gap areas of Can Gio mangrove forest after ten years of Durian typhoon

Perisesarma eumolpe is the dominant crab species in the Can Gio mangrove forest, which is affected by bidirectional interaction with the natural environment. After 10 years of Durian typhoon, Perisesarma eumolpe has had significant changes and adaptations on its growth in Can Gio mangrove forest. One of the main changes is their diets between the intact forest and the gap areas which are natural reforestation. The dry season results showed that the fullness of the stomach (S4) was the highest in the total analyzed stomaches. The fullness of the stomach of the P. eumolpe in the gap area (Hcut) is always higher than the rest area. The main diet composition of the P. eumolpe are seven food categories: decomposed leaves, bark, wood, animal debris, algae, sand, unidentified debris. Leaves are dominant food category in both forest and gap areas. To compare with the result obtained in 2007, the feeding ecology of P. eumolpe was initially recorded. These are the increase in stomach fullness, leaves are dominant in the gap area. There are the positive results from the natural reforestation of Can Gio mangroves in the gap area caused by Durian typhoon.

Diet and feeding ecology of Eriocheir sinensis on the Polish coast of the Baltic Sea and in the Tagus Estuary, Portugal

The feeding ecology of the Chinese mitten crab Eriocheir sinensis was studied by analyzing the stomach fullness and its content with regard to sex, size and brackish water habitats occurring on the coast of the Baltic Sea (Gulf of Gdańsk and Vistula Lagoon, Poland) and the Atlantic (Tagus Estuary, Portugal). The presented results show that neither the site, sex (except the Gulf of Gdańsk) nor the size of an individual had a significant (p > 0.05) effect on the stomach fullness of E. sinensis. However, the type of food consumed was significantly (p < 0.05) correlated with the inhabited locality. The stomachs of crabs contained the remains of animal and plant origin, as well as detritus. The remains of animals (Bivalvia, Amphipoda, Gastropoda and Polychaeta) were more frequently found in the crabs from the Gulf of Gdańsk, while the remains of plants (Tracheophyta, Chlorophyta) were most often found in the stomachs of crabs from the Vistula Lagoon and the Tagus Estuary. Detritus was found only in the Gulf of Gdańsk and the Vistula Lagoon. Research indicates that the feeding ecology of omnivore E. sinensis is habitat specific, which should be taken into account when assessing the risk associated with this invasive species.

Life history genomic regions explain differences in Atlantic salmon marine diet specialization

Animals employ various foraging strategies along their ontogeny to acquire energy, and with varying degree of efficiencies, to support growth, maturation and subsequent reproduction events. Individuals that can efficiently acquire energy early are more likely to mature at an earlier age, as a result of faster energy gain which can fuel maturation and reproduction.We aimed to test the hypothesis that heritable resource acquisition variation that co-varies with efficiency along the ontogeny would influence maturation timing of individuals.To test this hypothesis, we utilized Atlantic salmon as a model which exhibit a simple, hence trackable, genetic control of maturation age. We then monitored the variation in diet acquisition (quantified as the stomach fullness and composition) of individuals with different ages, and linked it genomic regions (haploblocks) that were previously identified to be associated with age-at-maturity.Consistent with the hypothesis, we demonstrated that one of the life history genomic regions tested (six6) was indeed associated with age-dependent differences in stomach fullness. Prey composition was marginally linked to both genomic regions (six6 and vgll3). We further showed Atlantic salmon switched to the so-called “feast and famine” strategy along the ontogeny, where older age groups exhibited heavier stomach content, but that came at the expense of running on empty more often.These results suggest genetic variation underlying resource utilization variation may explain the genetic basis of age structure in Atlantic salmon. Given that ontogenetic diet has a genetic component and the strong spatial diversity associated with these genomic regions, we predict populations with diverse maturation age will have diverse evolutionary responses to future changes in marine food-web structures.