#15 and 16. Reproduction - Review - The role of reproduction is to provide for the continued existence of a species; it is the process (either asexual or sexual) by which living organisms produces one or more individuals similar to itself - Animals compete with other individuals in the environment to maintain themselves for a period of time sufficient to enable them to produce tissue nonessential to their own survival, but indispensable to the maintenance of the species - Unlike most other organ systems, the reproductive systems of higher animals have not generally become more complex than those of lower forms - Note: Student should be familiar with differences between meiosis and mitosis, haploid and diploid (these concepts are included in BIO200), but we can refresh basic concepts. Students can also watch an easy podcast on meiosis and mitosis by Paul Andersen (Bozeman Science)–see links of interest - Different reproductive strategies: asexual vs. sexual (Ch 50, pp 1014-1018) - Asexual reproduction - Asexual reproduction is usually based on mitosis and results in offspring that are genetically identical to their parents. - Individuals clone themselves - Asexual reproduction involves the formation of individuals whose genes come from a single parent. There is no fusion of sperm and egg - Asexual reproduction occurs mostly in invertebrates (EXCEPIONS: sawfish, sharks –see links of interest-, some lizards. Attention: in some books/websites it is stated that only invertebrates have asexual reproduction, that is not true) - Mechanisms of asexual reproduction (Examples in Ch 50, pp 1014, Fig. 50.1) - Diverse mechanisms of asexual reproduction enable animals to produce identical offspring rapidly - Budding - Fission - Parthenogenesis (literally, “virgin origin”) - Case study: Switching reproductive modes. Daphnia switching from parthenogenesis (favorable conditions) to sexual reproduction (environmental stress) (Ch 50, pp 1014-1015, Fig. 50.2) - Why do daphnia switch between asexual and sexual reproduction? - Sexually produced offspring is are genetically diverse - Genetically variable offspring have higher fitness in environments with rapidly evolving parasites, deteriorating physical conditions, or other types of rapid environment change - See also cases of virgin births in sawfish and sharks (and their ecological impact) in links of interest - Sexual reproduction - Sexual reproduction is based in meiosis and fusion of gametes - Due to genetic recombination during meiosis and the fusion of haploid gametes –usually from different parents- during fertilization, sexual reproduction results in offspring that are genetically different from each other and from their parents - The mitotic and meiotic cell divisions and developmental events that produce male and female gametes, or sperm are eggs, are collectively called gametogenesis: spermatogenesis is the formation of sperm and oogenesis is the formation of eggs (Ch 50, pp 1016, Fig. 50.4)-Well see the endocrine control of these processes at the end of this lecture - Fertilization (Ch 50, pp 1018-1021) - Fertilization is the joining of a sperm and an egg to form a diploid zygote - There are two basic ways in which egg cells and sperm cells are brought together: 1) external fertilization, in which both types of gametes are shed into water and the sperm swim or are carried by currents to the eggs; and 2) internal fertilization, in which the eggs are retained within the reproductive tract of the female until after they have been fertilized by sperm inserted into the female - External fertilization - External fertilization is limited essentially to animals living in aquatic environments. The flagellated sperm must have fluid in which to swim, and the eggs lack a protective coat or shell (so that sperm can penetrate and fertilize them), and would dry out in the air - Shedding eggs and sperm into the water is an uncertain method of fertilization: many of the sperm never locate an egg, and many eggs are never fertilized, even if both types of gametes are shed at the same time and in the same place, as is usually the case. Consequently, animals using external fertilization generally release vast numbers of eggs and sperm at one time: - Given that sperm and eggs from different individuals must be released into environment synchronously for external fertilization - Gametogenesis occurs in response to environmental cues, such as lengthening days, temperature or warmer water temperatures, which indicate a favorable season form breeding - Season and rhythms in aquatic environments (see “Another place, another timer: marine species and rhythms of life” -in links of interest) - Gametes are released in response to specific cues from individuals of the same species - Pheromones provide information about members of the same species (Ch 47, pp 966-967) - Pheromones in aquatic environments (Ch 48, pp 1018-1019) - How do gametes from the same species recognize each other? (Ch 23, pp 421) - Internal fertilization - Most land animals, both invertebrate and vertebrate, use internal fertilization. In effect, the sperm cells are provided with the sort of fluid environment that is no longer available to them outside the animals’ bodies - Once fertilized, the egg is either enclosed in a protective shell and released by the female, or held within the females’ body until the embryonic stages of development have been completed - Internal fertilization also requires close physiological and behavioral synchronization of the sexes, which involves extensive hormonal control - Males deposit sperm into a female using an intromittent organ (e.g., hectocotylus in mollusks, claspers in Chondrichthyes, penis in higher vertebrates) - Males package their sperm into spermatophores, which is place into the female repro tract by female or male. - Why do some female lay eggs while others give birth? (Ch 50, pp 1020-1021) - For females, many aspects of fertilization and egg laying vary among species: for example, a female’s size of age at first breeding (i.e., puberty): the number of eggs that produces; the number of times she reproduces over the course of a lifetime - Oviparous-There’s a typo in wikipedia - Viviparous - Ovoviviparous - Natural selection favors live birth in cold habitats - Other reproductive strategies in aquatic environments - Semelparity and Iteroparity - Anadromy and Catadromy - Gonochorism and hermaphroditism - Hermaphroditism: Protogyny and Protandry - In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together - Internal self-fertilization may occur in some other species - Sexual parasitism - Sharks and rays as examples of diversification of reproductive strategies (see links of interest) - Compare advantages and disadvantages of each strategy - Endocrine control of reproduction in vertebrates (Ch 50, pp 1025-1027) - Brain-pituitary gonad axis - Environmental cues - Pituitary gonadotropin-gonad sex steroid signaling - Oogenesis - Primary growth - Secondary growth - Maturation, ovulation and spawn - Spermatogenesis - Spermatogonial proliferation - Spermiogeneis - Spermiation and spawn - Links of interest - Mitosis and Meiosis by Paul Andersen (Bozeman Science) https://www.youtube.com/watch?v=2aVnN4RePyI - Giant sawfish have virgin birth, rewrite biology text books http://www.livescience.com/51032-sawfish-have-virgin-births.html - Virgin birth in a shark http://www.sciencedaily.com/releases/2008/10/081010173054.htm - Comparison sexual vs. asexual reproduction http://www.diffen.com/difference/Asexual_Reproduction_vs_Sexual_Reproduction - Shark and ray reproduction http://www.sharksavers.org/en/education/biology/shark-and-ray-reproduction/ - How shark penises evolved http://news.sciencemag.org/biology/2015/04/how-shark-penises-evolved - Why researchers are super excited they saw this whale’s penis http://www.huffingtonpost.com/2015/04/24/humpback-whale-penis_n_7132628.html - Another place, another timer: marine species and the rhythms of life –an interesting review on chronobiology http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3182551/ #EXAM #Lab work To be determined