Question

explain reproductice strategies (behavioral & physiological) in different marine mammal groups. your answer should include a discussion of lactation energetic strategies as well.

Answer 1

The evolutionary order of the marine mammals is Carnivora (Pinnipedia), Cetacea (Mysticeti), Odontoceti, and Sirenia (Trichechidae, Dugongidae). Marine mammals are basically well known aquatic mammals such as polar bears, whales, seals, sea otters, etc. Polar bears spend most of their time in water, but they need to move to the ice for giving birth. Sea otters able to move from water onto the land, and their reproduction process is totally in the water. They have a lengten their reproductive cycle with an inter-birth interval of about one year sometimes two years. As mammals, these animals have to give birth to live new offsprings and produce milk to nourish their offspring. Although photoperiods are a major contributor to breeding period regulations of these mammals, additional environmental factors effect the breeding season. For few species the environmental factors may be the primary determinant of the seasonal breeding period. Reproductive cycles of most of the pinniped species are regulated by photoperiods, but events such as scarcity or malnourishment can lead to anestrous in the female. In the case of cetacean species, various environmental conditions such as food, and prey availability,and physical condition of the female, weather conditions, and location of predators have influence on the female reproductive cycle than the photoperiod.

Characteristics of marine mammal (male) reproduction system

Usually they have an increase testicular size and mass that correlates positively with an increase in ejaculate volume. Sperm competition refers to polyandry that is matings of the same female by different males of the same species. Males with higher concentrations of viable, morphologically normal sperm will have a greater chance of passing their genetic information on to the next generation. The main hormone in male marine mammals is the androgen testosterone. Testosterone is responsible for the stimulation of spermatogenesis and levels of testosterone are found to increase with time.The increase in testosterone levels is used to predict the sexual maturity of a male given there is a defined definition for sexual maturity. Sexual maturity in some species of marine mammals is determined by the point at which sexual dimorphism of size in favor of the male is apparent. Sexual dimorphism refers to the phenomena where males and females of a same species can be differentiated. The majority of marine mammals (males) are typically larger than females where sexual dimorphism is observed.

Behavioral Changes

During the transition from the non-breeding season to the breeding season, male marine mammals undergo various changes in behavior. One behavioral change is a reduction of energy expenditure. This is most likely because males are not producing milk during the breeding season as females do. In some species, including earless seals, males fast maximize access to sexually receptive females.[3] There is a limit however, and when the male's fat content drops to a level at or below the levels found in the receptive female, the male will discontinue fasting and stop all breeding behaviors, such as aggressive behavior.

Males are more aggressive to other males and sometimes the female during the breeding season. Males compete against each other to access females and this aggression improves their ability to breed with the female of their choice or even multiple females and then defend these females against other males. To help defend against the other males, evolutionary pressure has selected traits that support sexual dimorphism. While actual physical aggressive behavior is relatively common in certain species such as pinnipeds (sea lions). However, pinnipeds females are almost always injured or sometimes even killed during mating attempts due to physical aggression.

Physiological Behaviors

Some marine mammal species undertake physiological changes during the breeding season. This can be seen in some pinniped species where vocal signaling strength increases or emissions of strong odors are released to attract the female. The strong odor is the result of the enlargement and increased activity of sweat glands surrounding the muzzle. When fat levels drop towards the end of the breeding season, the strength of the odor and vocal emissions also decrease. Additionally, in the transition to the non-breeding season, testosterone levels generally decrease. This can be attributed to a decrease in testicular size associated with the non-breeding season along with a decrease in testicular size.

Characteristics of marine mammal (female) reproduction system

The female marine mammal reproduction tract is similar to the terrestrial mammal. The main difference is the lower portion of the posterior fanny in the seal. The seal has a genital lock system consisting of hymeneal folds and muscle tissue. The main purpose of the genital lock system is to prevent water and debris from entering after copulation by the male. Female marine mammals also contain a cervix, a bicornuate uterus consisting of one uterine body and two uterine horns, two oviducts, and two ovaries.

Hormonal Changes

The marine mammal estrous cycle consists of two phases: the follicular phase and the luteal phase. The characteristics of these phases are similar to terrestrial mammals. The follicular phase is characterized by a large rise in estradiol, which stimulates the release of GnRH. The GnRH surge allows the release of FSH, which causes tertiary follicles to develop into dominant follicles. An LH surge causes ovulation to occur. The length of the follicular phase varies by species. The luteal phase is characterized by the rise of progesterone and the decrease of estradiol. Shortly after ovulation, a corpus luteum forms on the ovary where the egg was ovulated from. The corpus luteum then produces progesterone which inhibits estradiol and GnRH so ovulation cannot occur. Progesterone calms muscular contractions in the uterus so pregnancy can be maintained if fertilization has occurred. The luteal phase also varies depending on the species in terms of length.The phase can be anywhere from fifteen days to several months. If the length of the luteal phase is months, it is generally the result of pseudopregnancy. Pseudopregnancy is defined as the prolonged period of high concentrations of plasma progesterone in animals that are not carrying a fetus. These females will return to estrous during the breeding period.The female reproductive cycle is regulated mainly by photoperiod, but other environmental factors may play a role. In some species, environmental factors may be the primary determinant of the season.

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