Animals somehow "know" that, during their lives, the most important operation is to perpetuate their own species, giving birth to new generations. Here arises an important dilemma that characterizes the life history of the species: giving birth to many offspring with the hope that at least someone will survive, or just a few, following them step by step until they are able live safe on their own? This is an important parameter that have influenced - and still influence today - the biology and the ecology of animal species. It is a matter of energy investment. In summary, we could say that, as animals become more evolved, the second strategy is "preferred" to the first. Invertebrates and in general amphibians, reptiles and most fish species produce many eggs, but they are abandoned to their fate. There are so many that, statistically, some will manage to survive, and the offspring will become adults. Among mammals, on the contrary, we find the maximum development of "parental care", in other words, the behaviours played by adults that give the chance to newborns to reach adulthood. Depending on the species, those behaviours can be played by females on their own, in collaboration with males or other kin related females.  Female of striped dolphin (Stenella coeruleoalba) with her newborn - Photo by Stefano Bellomo In biology, the first strategy is called "r-selection": adults produce many offspring, each of which has a relatively low probability of surviving to adulthood. The losses are very high, but, in return, adult individuals have spent only the energy necessary to produce the eggs. An example is the Sunfish (Mola mola): each female can produce up to three hundred million eggs during their life cycles.  Sunfish (Mola mola) - Photo by Stefano Bellomo The second strategy is defined "K-selection": each female produces a limited number of offspring but dedicates to each of them a great deal of time, attention, energy, resources. Humans, apes, birds of prey, elephants and cetaceans are typical K-selected species. In my experience studying cetaceans in the Gulf of Taranto, I was lucky enough to be able to observe calves of three different species many times: bottlenose, striped and Risso’s dolphins. For all cetaceans, the birth is podalic, that means that the calves born from the tail and are already able to swim to follow the mother that after birth accompanies the calf to the surface to make it breathe. In this operation sometimes the mother is assisted by other females, generally kin related.  Bottlenose dolphin calf (Tursiops truncatus) - Photo by Stefano Bellomo For the first few hours of life the dolphin's dorsal fin is not yet sturdy and hoisted upwards but is folded back on itself. They swim a little breathless accompanied by mothers who gently help them stay afloat and breathe. After approximately 48-72 hours, their dorsal fin is straight like the one of their mothers but another morphological element (apart for the small size) can characterise a newborn: the "fetal folds". In other words, the folds of the skin, a feature in common even to newborn children.  Bottlenose dolphin calf (Tursiops truncatus) - Photo by Stefano Bellomo Thanks to the observation of these details and thanks to the photo-identification of the mothers, we can observe the mother-calf relationships over the years. Females of striped and bottlenose dolphins reach sexual maturity between 5 and 13 years of life and the females of Risso’s dolphins between 8 and 10 years of life.  Striped dolphin newborn (Stenella coeruleoalba) - Photo by Stefano Bellomo The gestation lasts between 12 and 14 they almost always give birth to only one calf. The weaning period is around 16-18 months and the calves remain with their mothers up to about 6 years of age. Between one gestation and another there is a pause of 2-4 years. Breast milk of cetaceans contain a high percentage of milk fat and it accelerates the growth of calves during their first moths of life, in order to become fast swimmer as soon as possible, to be able to always follow their group and to avoid predators such as big sharks or killer whales.  Striped dolphin calf (Stenella coeruleoalba) - Photo by Stefano Bellomo Because young offspring are not very proficient divers, females often reduce the number or duration of foraging dives. Cetaceans have little or no sense of smell (absent in odontocetes; rudimentary in mysticetes), but likely use acoustic communication for individual identification. Delphinids produce a diverse array of sounds, including echolocation clicks, burst-pulse sounds, and whistles and they develop signature whistles in the first years of life. Field studies suggest that whistles mediate natural separations and reunions between mothers and calves. Mothers influence offspring behavioural development by the experiences they provide, including migration and navigation, communication, social interactions, and foraging.  Risso's dolphin calf (gray) with two adults (Grampus griseus) - Photo by Stefano Bellomo Striped dolphins and Bottlenose dolphins have a very intense social life, defined as "fission-fusion". In short, the social life of these animals is characterized by the continuous meeting and separation of family groups that in the area of the Gulf of Taranto, come together to socialize and separate to hunt. The calves of these two species, once they become sub-adults and then adults, over all males, tend to separate from the original group to join other groups or other individuals of the same sex and of the same age, continuing to live in a very dynamic and fluid society. Rissso’s dolphins are characterized by a less dynamic society, in which females tend to stay more with the group they belong to. The significance of such long-term kin associations offer the benefits of group living. Such benefits include protection from predators or conspecifics and sharing of information and tasks, such as calf care.  Risso's dolphin calf (Grampus griseus) - Photo by Stefano Bellomo In sum, marine mammal mothers invest extensively and exclusively in single offspring. In the following photographs I show you the underwater mother-calf connection of "Surf", a Risso's dolphin mother, with her curious and funny calf, named "Mario". This photograph was shooted in summer 2018, when they have been observed for the first time together.  Mario, the Risso's dolphin, photographed during his first sighting in 2018 - Photo by Stefano Bellomo After that, in April 2019 the little Mario had grown up. We initially sighted him while swimming alone in the bow waves of our boat. Immediately, next to him appeared his protective mother "Surf", never letting him going too far alone.  Mario with her mother Surf - photographed in summer 2019 - Photo by Stefano Bellomo Their preservation its crucial for the survival of the whole marine ecosystem. Please, if you want to enjoy the emotions to see dolphins and whales, never go to captivity shows. What you see there, is not their real life. Moreover, be aware to choose dolphin & whale watching sustainable tours that do not stress or harm wild animals.  The curious Mario approaching the camera during one of the last sighting in 2019 - Photo by Stefano Bellomo I am really lucky to have the chance to study and observe these animals in the years, free in their natural habitat. If you want to support the conservation efforts of our team, the Jonian Dolphin Conservation, you can do it in many ways. It's possible to adopt some of the dolphins that we have observed and catalogued and, one of them, is my beloved Mario.
I will keep you posted about new blue stories... Stay tuned! I commenti sono chiusi.
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