User:Amercoli/sandbox/Cetacean Infanticide

Infanticide (Cetacean)

Background:

Infanticide can easily be defined as the killing of offspring by and adult animal of the same species. This can appear as a cruel act in nature but the reasoning behind this act is not as far fetched as one might think. The two main causes of it are social interactions in the population and the strategies each species uses to reproduce. This leads to infanticide usually being more prevalent in species with a lesser male population. In lesser male populations they have to compete for mates and resources alike in order to reproductive. This is referred to as sexual conflict an example of that is a population where traits that increase a male’s fertilization success during sperm competition can be harmful to females. Species that commit infanticide include but are not limited to Bottlenose Dolphins, Black Guillemots, and Black-tailed Prairie Dogs.

Another example of infanticide that is prevalent is filial infanticide. Filial infanticide is not only the killing off of offspring in the same species but it is the the killing of offspring by their own parents. The methods could even include the abandonment of your offspring all together. This behavior is most common in fish and cetacean species.

Examples:

Infanticidal behavior is not adapted but instead the aberrant aggressive response to the overpopulation and crowding that can occur. It is also observed by committing infanticide, the males might cause the baby-less females to resume ovulating, which would not happen for several years in females that are nursing. Infanticide can be linked to the arrival of a new male or males into a band of females, with the associated ejection of the father or fathers of any offspring in the group. New males could father offspring more quickly if they first killed the infants in the band. Females who lose their infants do resume ovulating, and that enables the new males to become fathers for their replacement offspring. This behavior has been shown in primates, various carnivores, horses, rodents, and even bats. Hormonal modulation of behavior could in species, such as mice, in which during the infanticidal phase, the brains of male mice are more receptive to progesterone which in turn increases the likelihood of killing their offspring [ ].

This behavior, as previously mentioned, can occur in an array of species. Male bottlenose dolphins try to drown their pups no more than two minutes after. It has been suggested that infanticide may be an important factor in shaping the social structure of the bottlenose dolphin, as well as other cetacean species, but could also play a major impact into the viability of small populations. The aggressive interaction that can be observed in interspecific interactions. Males helping with the act of killing an offspring, mating strategies have resulted in alliance formation to heard females [Patterson I a. P, Reid RJ, Wilson B, Grellier K, Ross HM, Thompson PM. 1998. Evidence for infanticide in bottlenose dolphins: an explanation for violent interactions with harbour porpoises? Proc R Soc Lond B Biol Sci. 265:1167–1170. doi:10.1098/rspb.1998.0414.].

Another example of infanticidal behavior occurs in black guillemots due to the overpopulation leading to food shortages. Chicks that were left unattended in areas of higher density were more likely to be attacked and killed. Chimpanzees display the same tactic in attacking infants that are left unprotected. Males from one group will strike out at males in other group leaving unattended infants. In both cases these animals resort to cannibalism when food shortages occur [ ].

Female black-tailed prairie dogs kill offspring of close relatives.These females typically lactate when displaying infanticidal behavior. Lactation occurs due to the stress these females endure to provide for their own young. Although it is more common for female black-tailed prairie dogs to kill offspring, male black-tailed prairie dogs become infanticidal with the offspring of the females they have mated with. Females are able to give birth to a litter of pups with more than one father and it is observed that, unlike in mice, these males are able to tell which pups are theirs [ ]. Female meerkats display similar to behavior to the female black-tailed prairie dogs. Dominant females will kill the young of subordinate females. The dominant female with then force the subordinate female to become a ‘wet nurse’ and feed her young. The behavior ensures that competition for her own young is reduced as well as, securing food for her young [ ].

In hanuman langurs infanticide might have spread through the populations due to the reproduction-enhancing tactics for individuals males that have been observed. Dominant males will kill any preexisting infants to prepare for his own offspring. Killing the offspring of the females will lead them to become reproductively responsive since they are no longer nursing [ ]. This behavior is displayed in lions and chacma baboons as well.

Cetacean Background:

Marine mammals are an extremely important for aquatic ecosystems. Cetaceans are a family of marine mammals that can be found in most waterways and each ocean throughout the entire world. Species that fall under the cetacean family are whales, dolphins, and porpoises. Although these animals spend all of their lives in Open Ocean and wide bodies of water, they are mammals just like human beings. They are warm-blooded creatures that give live birth and even nurse their young through to their juvenile stages. Marine mammals even have traces of hair and require oxygen from the air as they have lungs just like terrestrial mammals.[ ] It has been observed that marine mammals were once terrestrial themselves, which is why they share many of the same traits as humans and other terrestrial mammals. The bone structure of marine mammals is also very similar to the structure of the limbs of terrestrial mammals.[ ] Marine mammals have been able to develop a circulatory system that allows for the storage of more oxygen in the blood and they even produce higher volumes of blood in relation to their body size when compared to land mammals. There are two types of cetaceans, those being the toothed whale (odontocetes) and the baleen whale. Odontocetes have openings on their blowholes, as well as teeth, they travel in groups, and they use echolocation to travel and communicate. Baleen whales have several layers of baleen teeth, two blowholes, and they eat krill rather than meat. Many cetaceans are endangered and their numbers continue to decrease. Ship strikes, disease, commercial whaling, plastics (PCBs), and fishing nets cause these whales to die off every year. Thousands are killed a year by fishing nets and plastic netting alone. The ship strikes and motors of cruise ships, sonar of submarines, and loud noises of other large vessels cause the cetaceans to lose their ability to echolocate as well. This leads to strandings and starvation in many cases. Many cetaceans, ie. Humpbacks, have very fragile inner ears that can be easily damaged by loud noises and heavy vibration. Damage to the inner ear also causes the cetaceans to lose the ability to maintain their balance in the water. These are all issues that can be prevented by human interaction, however, what if the cetaceans themselves are damaging their own kind. There have been several reports suggesting that cetaceans actually will kill off other members of their community and other members of their species. Some suggest the cetaceans may be committing acts of infanticide. There are several reports to back this theory.

Cetacean Infanticide:

Killing of dependent infants by conspecific males, referred to as ‘‘male infanticide,’’ represents an explicit example of sexual conflict, which arises when the reproductive strategies of one sex impose fitness costs on the other [ ].

In killer whales observations of infanticide specifically in males can be linked to key morphological traits that male killer whales may be sexually selective toward for more reasons than influencing female choice in mates [ ].

For some social networks of killer whales where they are targeted for individual captivity, the killer whales may be forced to perform infanticide from indirect hunting habits [ ].