Intraspecific Cannibalism Research Articles

What Causes Differences in the Age-Class Structure between Suburban and Forest Populations of Anolis homolechis?

Although growing urbanization has direct negative consequences for local biodiversity, several native species have been observed maintaining populations in urban environments. Understanding which factors influence the ability of native species to persist in urban environments is crucial, both for the study of biological adaptation and of urban planning. The quantification of the proportion of juvenile individuals can be a good proxy for assessing the long-term persistence of urban populations. We present comparative data about spatial and temporal variations in the age-class structure in two suburban and two forest populations of the Cuban endemic lizard Anolis homolechis, obtained during a 20-month survey. We found a four-fold lower proportion of juveniles in the suburban habitat compared to the forest one. There was, however, no evidence for differential female fecundity between the two habitats, as assessed by the proportion of gravid females. Conversely, the rate of tail autotomy (an antipredator behavior) was significantly higher in the suburban juveniles compared to the forest ones, possibly reflecting a higher exposure to predators and, particularly, inter- and intraspecific cannibalism. However, tail loss at initial capture or habitat type had no effect on the probability of recapture of juveniles. We discuss the potential causes and consequences of a modified age-class structure in urbanized environments.

Intra- and inter-specific interactions between <i>Coccinella transversalis</i> and <i>Cheilomenes sexmaculata</i> in relation to prey abundance

In the present study, we investigated the feeding rate and the effect of intra- and inter-specific interactions between adults, 3rd and 4th instar larvae of the coccinellids, Coccinella transversalis and Cheilomenes sexmaculata to its conspecific and heterospecific combinations under laboratory conditions. Cannibalism and the effect of interaction were investigated using the multiplicative risk model. Aphidophagous predators and their instars were kept alone, paired with conspecifics, and heterospecifics combinations in the absence and presence of prey (aphid, Aphis gossypii). In the presence of aphids, the combined release of these predator species revealed that except for (3rd × 3rd) and (4th× 4th) intraspecific combination of both predators, the observed consumption was lower than the expected consumption. In the case of interspecific combination, the observed consumption was significantly lower than expected and it indicated the antagonistic effect of both the predators in later instars in the presence of sufficient prey population. In the absence of the prey, intra-specific cannibalism was lowest between adults of both the species and highest among C. transversalis 3rd × C. transversalis adult and C. sexmaculata 3rd × C. sexmaculata adult. The interspecific predation was highest between C. transversalis adult × C. sexmaculata 3rd instar and lowest between adults of both species. The results suggest that C. transversalis was more a successful aphid predator, being able to find aphids more quickly and consume more of them compared to C. sexmaculata. As there was less intraspecific cannibalism among C. transversalis and individual consumption is also high, it is considered to play a significant role as a biocontrol agent in aphid management.

Growth, Cannibalism, and 5-TH Metabolism in Pufferfish (Takifugu obscurus ♀ × Takifugu rubripes): The Role of Graded Levels of Dietary Tryptophan.

The objective of this study was to investigate the potential effect of graded levels of tryptophan on the growth, cannibalism, and 5-hydroxytryptpamine (5-TH) metabolism in pufferfish (Takifugu obscurus ♀ × Takifugu rubripes ♂). A 63-day feeding trial was performed wherein pufferfish were fed four diets. Three experimental diets were formulated with various levels of tryptophan based on the control diet. Four diets were named as T1, T2, T3, and T4, corresponding to 4.30, 7.80, 14.90, and 23.70 g kg-1 tryptophan of dry diet. Final body weight, weight gain, and specific growth rate were similar between the T1 and T4 groups, but exhibited a significantly increased trend compared to the T2 group. Although survival rate was not affected by various levels of dietary tryptophan, intraspecific cannibalism was significantly reduced in the group fed with highest level of tryptophan (T4). For free amino acid in brain, the concentration of tryptophan was the highest in the T3 group and the lowest in the T2 group, while phenylalanine, tyrosine, and methionine showed an opposite trend between those two groups. The levels of dietary tryptophan not only affected the expression of aromatic amino acid transporter TAT1, but also affected the expression of B0AT1, B0AT2, and 4F2hc in intestine, as well as B0AT1, y+LAT1, and LAT2 in brain. The activity of tryptophan hydroxylase (TPH) in serum increased with the increase of dietary tryptophan, and the expression of TPH1 in brain upregulated in the excessive tryptophan groups (T2, T3, and T4). MAO activity in serum as well as its gene expression in brain and intestine showed a decreased trend in the T4 group. In conclusion, excessive tryptophan (23.70 g kg-1 of dry diet, corresponding to 50.3 g kg-1 of dietary protein) in feed could mitigate cannibalistic behavior of pufferfish and promote the growth, and the reason for this effect might affect the metabolism of 5-TH in vivo.

Age structure affects population productivity in an exploited fish species

Long-term changes in the age and size structure of animal populations are well documented, yet their impacts on population productivity are poorly understood. Fishery exploitation can be a major driver of changes in population age-size structure because fisheries significantly increase mortality and often selectively remove larger and older fish. Climate change is another potential driver of shifts in the demographic structure of fish populations. Northeast Arctic (NEA) cod is the largest population of Atlantic cod (Gadus morhua) and one of the world's most important commercial fish stocks. This population has experienced considerable changes in population age-size structure over the past century, largely in response to fishing. In this study, we investigate whether changes in spawner age structure have affected population productivity in NEA cod, measured as recruits per spawning stock biomass, over the past 75 years. We find evidence that shifts in age structure toward younger spawners negatively affect population productivity, implying higher recruitment success when the spawning stock is composed of older individuals. The positive effect of an older spawning stock is likely linked to maternal effects and higher reproductive output of larger females. Our results indicate a threefold difference in productivity between the youngest and oldest spawning stock that has been observed since the 1950s. Further, our results suggest a positive effect of environmental temperature and a negative effect of intraspecific cannibalism by older juveniles on population productivity, which partly masked the effect of spawner age structure unless accounted for in the model. Collectively, these findings emphasize the importance of population age structure for the productivity of fish populations and suggest that harvest-induced demographic changes can have negative feedbacks for fisheries that lead to a younger spawning stock. Incorporating demographic data into harvest strategies could thus facilitate sustainable fishery management.

Observations of the mating behavior of Portunus trituberculatus and the role of shelters in its mating process

In this study, the mating behavior of Portunus trituberculatus under indoor conditions and the role of shelters in its mating process were systematically studied by using behavioral observation methods. The results showed that the mating behavior of P. trituberculatus was divided into four stages: courtship and pre-copulatory guarding, reproductive moulting, copulation, and post-copulatory guarding. P. trituberculatus in the no shelter group (NSG) usually preferred to gather at the edges or corners of the cement tank, while P. trituberculatus in the shelter group (SG) preferred to hide in the shelters. During the whole experiment, the shelter occupancy rate of P. trituberculatus during the day (57.40%) was significantly higher than that at night (38.08%) (P < 0.05). In terms of hiding rate, the hiding rate was as high as 63.32% during the day, which was significantly higher than that at night (37.70%) (P < 0.05). The copulation time of the SG was similar to that of the NSG. However, the durations of the pre-copulatory guarding period and post-copulatory guarding period of the SG were shorter than those of the NSG, indicating that the presence of shelters could shorten the total mating duration of P. trituberculatus. P. trituberculatus provided with shelter did not hinder its mating behavior, and there was little difference in mating rate between NSG and SG, which were 100% and 97.22%, respectively. In addition, we found that there was certain cannibalism during the reproductive moulting of female crabs, which could lead to the death or injury of some individuals. However, the survival rate of the SG (89.58%) was significantly higher than that of the NSG (72.92%) (P < 0.05). Moreover, the injury rate in the SG was only 14.13%, which was significantly lower than that in the NSG (31.31%) (P < 0.05). In general, shelters have the capability of appealing to P. trituberculatus during mating and can effectively reduce the incidence of intraspecific cannibalism during mating and improve the survival rate of P. trituberculatus.

Egg Predation by the Introduced Lady Beetle, Coccinella septempunctata (Coleoptera: Coccinellidae), Lowers Mortality but Raises Relative Risk for the Native Lady Beetle, Coccinella novemnotata.

Populations of the native ninespotted lady beetle, Coccinella novemnotata Herbst, have undergone precipitous declines in North America following the establishment of the exotic sevenspotted lady beetle, Coccinella septempunctata L. Recent volunteer efforts have made it possible to establish colonies of the now-rare C. novemnotata and test mechanisms contributing to its decline. We evaluated the relative frequencies of intraguild predation and cannibalism of eggs between these two species. A single C. novemnotata or C. septempunctata adult was exposed to conspecific and heterospecific eggs in either the presence or absence of pea aphids. The study revealed two expected results: 1) eggs of C. novemnotata were consumed more frequently than eggs of C. septempunctata by both species, and 2) egg consumption was higher when aphids were absent, independent of predator and egg species. There were also two unexpected results from the study: 1) the asymmetry between egg predation rates was higher when aphids were present, and 2) higher predation rates on C. novemnotata eggs in the absence of alternate prey was due to a relatively higher rate of intraspecific cannibalism. This implies that C. novemnotata would have suffered higher egg mortality rates before the invasion of C. septempunctata, but even though the aggregate rate of egg predation on C. novemnotata eggs is lower post-invasion, it is still significantly higher than the aggregate rate of predation of C. septempunctata eggs. This differential pattern of asymmetric predation could contribute to habitat compression and the overall decline of C. novemnotata.

The effect of inter- and intra-specific competition on survival and growth rate of native juvenile noble crayfish Astacus astacus and alien spiny-cheek crayfish Orconectes limosus

Juvenile noble crayfish, Astacus astacus and spiny-cheek crayfish, Orconectes limosus were reared from the 2nd and the 3rd developmental stage (i.e. since the stage of independence), respectively, until the end of the growing season. The first period revealed very low survival rate of O. limosus in the communal stock (7 ± 6.2%), probably caused by predation of A. astacus. Separately reared O. limosus proved significantly higher survival rate (49 ± 9.2%) than those in the communal stock with A. astacus. The latter species also showed the highest survival rate in this case (90 ± 7.1%). This was not found to differ from the survival rate of separately reared noble crayfish (86 ± 3.1%). In general, both the significant effect of bigger size of A. astacus than that of O. limosus and higher intra-specific cannibalism of O. limosus were reflected during the first phase of rearing. Size and weight of both species were equivalent 11 weeks after hatching (8 weeks of rearing). The higher cumulative survival rate was reached in the intraspecific culture of A. astacus (90%) while low cumulative survival of both species was found in communal stock (less than 50%) in the second phase of rearing. At the end of the growing season, 19-week-old O. limosus attained a higher mean size and weight but were more variable in the group (29.3 ± 5.17 mm and 616.4 ± 412.53 mg) than A. astacus (21.2 ± 1.82 mm and 229.9 ± 59.45 mg). Single and communal stock did not differ. Growth of O. limosus was much faster than that of A. astacus.

Generation cycles in Indonesian lady beetle populations may occur as a result of cannibalism

Generation cycles, population cycles with a period of approximately one generation, have been observed in a variety of field and laboratory studies. Such dynamics are predicted to arise through the effects of resource competition and cannibalism or involve consumer-natural enemy interactions. We first show, using a new highly simplified model, that generation cycles are a very common outcome of strongly age-structured intraspecific interactions involving cannibalism. We then analyse a series of unique long-term time-series of ladybeetle (Coccinellidae) abundances from tropical Indonesia. Some of the time-series display clear generation cycles, and we argue that there is strong evidence that these are caused by intraspecific cannibalism.

Stadium‐specific transmission of endosymbionts needed for pederin biosynthesis in three species of Paederus rove beetles

Abstract Females of the rove beetle genus Paederus (Coleoptera: Staphylinidae) accumulate large amounts of the defensive compound pederin produced by an endosymbiotic bacterium. Pederin is transferred in the eggs, while the endosymbionts are transmitted via the egg shell. In all three species analyzed (P. melanurus, P. riparius, and P. sabaeus), descendants of aposymbiotic matrilines (lacking both endosymbionts and biosynthetic capabilities) acquire biosynthetic capability by the ingestion of eggs with endosymbionts during larval development. Successful colonization by endosymbionts depends on the number of eggs consumed and the age of the feeding larvae. During the adult stage, however, the females cannot acquire biosynthetic capabilities. Adult females are able to sequester pederin from eggs eaten, and they transfer the substance into their own eggs. Lack of intrinsic biosynthesis after ingestion of endosymbionts indicates that these are not biosynthetically active within the gut and have to reach an unknown internal location before completion of metamorphosis. These results are discussed with regard to the benefit of intraspecific cannibalism.

Predator‐prey system structure in patchy and ephemeral phytotelmata: Aquatic communities in small aroid axils

AbstractMechanisms allowing the persistence of an aquatic predator‐prey system in tiny pools (the mean ca. 0.5 ml) held by taro axils were analyzed from the viewpoint of temporal and spatial patterns of habitat use. Predatory larvae of a mosquito Topomyia tipuliformis concentrated in young axils, while 9 other taxa utilized both young and old axils or concentrated more in older axils. The total prey density was lower in axils with the predator but the density of each prey taxon (except for a few cases) and the number of prey taxa did not differ between axils with and without predators. This indicates that T. tipuliformis is a general predator and does not influence prey community organization through selective removal of particular prey taxa. Inter‐axil distribution of T. tipuliformis was aggregated in the first instar but uniform in the third and fourth instars due to intraspecific cannibalism, which assures the survival of a single individual under short food supply. Distributions of prey taxa were mostly aggregated, fitting the negative binomial distribution. Thirty seven out of 45 associations of 10 taxa were independent with 3 negative (between the predator and some late‐colonizing prey) and 5 positive (between some prey taxa) associations. Probabilistic refuges (produced by independent aggregated distributions) reduced interspecific encounters which may result in competition and predation, and thus probably facilitated prey coexistence. There was no evidence for the importance of predation in structuring the prey community. This system may be prey‐dominated in that predator persistence depends on prey community existence but prey community structure depends less on predation.

Aquatic arthropod communities in Nepenthes pitchers: the role of niche differentiation, aggregation, predation and competition in community organization.

The structure and organization of aquatic arthropod communities in Nepenthes ampullaria pitchers were studied at two sites (M in Malacca and K in Kuching) in Malaysia. The communities consisted mainly of aquatic dipteran larvae. Community M was dominated by a filter feeder, Tripteroides tenax, which reached a high density despite a strongly aggregated distribution. Community K had five trophic groups: carrion feeders, filter feeders, detritus feeders, nipping predators and hooking predators, each including multiple species. The summed density of filter feeders in Community K remained much below the level attained by filter feeders in Community M. Niche differentiation within each trophic group with regard to pitcher age and feeding behaviour was not sufficient to allow species coexistence through niche separation alone. Aggregated distributions directly reduced interspecific encounters. Nevertheless, species belonging to the same trophic group commonly shared the same pitcher, because of high occurrence probabilities of dominant species and positive associations between some taxa (due mainly to similar occupancies by pitcher age). Predator coexistence in Community K may have been facilitated by self-limitation of the large predators through intraspecific cannibalism strengthened by aggregation. Prey coexistence, on the other hand, may have relied more on population suppression by predation, especially the selective removal of old instar Tripteroides.