This Ant is an "Aphid Rancher." (SE Costa Rica)
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Reproduction is the biological process by which new individual organisms are produced. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. The known methods of reproduction are broadly grouped into two main types: sexual and asexual. Sexual reproduction results in increasing genetic diversity of the offspring by two parents. It is characterized by two processes: meiosis (halving of the number of chromosomes) and fertilization (combination of two gametes and the restoration of the original number of chromosomes). During meiosis, chromosomes usually cross over creating genetic recombination. Sexual reproduction is the primary method of reproduction for the vast majority of visible organisms, including almost all animals and plants. Asexual reproduction is a form of reproduction which does not involve meiosis (halving the number of chromosomes) or fertilization. It also involves only one parent. There are a couple forms of asexual reproduction: budding (divisional and transversal) and fragmentation. Many plants and fungi reproduce mostly asexually as well as bacteria, archaea, and protists. This pape
The most colorful and remarkable underwater occurrences known to man is coral spawning. Once or in some cases twice a year, on a very erotic evening certain coral species spawn. This spectacular event is described as the harmonious releasing of eggs and sperm by numerous colonies of different coral species. (Richmond, 1998) In Australia this event takes place five nights after the November full moon. In the Gulf of Mexico this event takes place on the eighth night after the August full moon. (Richmond, 1998) On the other hand, the wilder part of sex in vertebrates is sex determination. This is usually a fixed characteristic in terms of life history. Interestingly, there are a few organisms for whom sex is a fixed condition, often determined by a combination of internal and external signals. One such group of organisms which follows this trend is the tropical, conspicuous colorful fish inhabiting coral reefs.
Coral reefs are known for their diversity. This diversity evolves from organisms that can be pressured to changeÑand sometimes into entirely new speciesÑboth by the physical environment and by the organisms with which they interact. Just take a daytime dive on the reef to discover new species that have evolved as partners, adversaries, and enemies in the never-ending challenge to survive and reproduce.
On the reef there is a sexual dimorphism in many marine species. The first commonly known dimorphism is sexual versus asexual reproduction. The most commonly known species on the reef is corals. Corals are unique invertebrates because they can both sexually and asexually reproduce. Certain conditions can influence different spawning methods. Scientists do not understand exactly how the event is triggered, but experimentally understood that the spawning is triggered by a blue light from the moon. A certain gene prompts a series of biochemical reactions that make coral spawn. (Hansford, 2007) It is theorized that the position of the moon and its effect on the tidal currents is important for successful fertilization as well as later dispersion of the larvae. (Yao, 1995) This event of coral spawning has become a tourist attraction for divers in reefs all over the Caribbean.
Three of the most productive corals are the symmetrical brain corals (Diplora strigosa), the cavernous star corals (Montastrea cavernosa) and the mountainous star corals (Montastrea annularis complex). The great star corals have separate male and female colonies, while the other two species are hermaphrodites, which mean they have both male and female sex organs and can self-fertilize and cross-fertilize between colonies. (Yao, 1995) On the night of spawning, soon after sundown, the flower-like polyps which make up the living coral colony begin to expand, as sperm packets are moved up from a space within the underlying coral skeleton. Before the coral species release their eggs or sperm, many become puffy looking. Star coral polyps withdraw their tentacles, which is unusual since their tentacles are usually seen out at night. (Richmond, 1998) Male cavernosa star corals discharge their sperm in gushes that resemble puffs of smoke, while female corals release tiny spherical egg sacs. (Richmond, 1998) Brain corals have been noted to expel, from their intricate ridges, lines of eggs. In perfect synchronization tiny sperm and eggs burst free from coral species and start mass fertilization. (Richmond, 1998) Soon, bright orange or pink eggs are brought up and "glued" to the individual sperm bundles, until the sperm is completely surrounded. This is a nice trick, as these clusters of 9 - 190 eggs around a central sperm core, float to the surface due to the high fat content of the eggs. In this way, eggs and sperm from different colonies have a chance to intermingle at the ocean's surface, and if the combination is right, fertilization will take place. (Richmond, 1998) The water then becomes clouded by the tiny eggs and sperm. Planulae are created from fertilization that swim and drift in the currents for generally three to four weeks before eventually settling on the bottom of an open area of hard bottom or bare substrate. Then they fuse to form new colonies of coral. It has been reported that coral spawning triggers other sea creatures to spawn, such as tree tube worms, wrasses and cowfish. (Yao, 1995)
One interesting experiment happened in a research center in Guam with getting sperm from one species to fertilize eggs of related but different species. This is called hybridization, and such crosses may be one reason for the wide variety of coral forms on the reef. (Richmond, 1998) One new species that has arisen from hybridization of Elkhorn coral ÂAcorpa palamta and staghorn coral Acorpa cervicornis is called fused Elkhorn Acorpa prolifera. Reef-building corals may live for several decades or centuries, so these ÒimmortalÓ hybrid lines accumulate over time. (Reinert, 2002) Just as the corals reproduce sexually by releasing their gametes into the water, so does both sea urchins and sea cucumbers. (Bhamrah, 2002)
If the conditions arenÕt perfect, then coral will reproduce asexually: division budding (longitudinal and transversal) and fragmentation. In the process of budding, a young coral individual grows out from the adult (parent) polyp, this is the way a colony grows. Within the reach of the mouth or the tentacles of an adult polyp, a daughter polyp forms. As the daughter polyp grows, it produces a coelenteron, tentacles and a mouth. Sometimes, the young polyp can originate beyond the wreath of tentacles. When this happens, the distance between the polyps increases which causes development of coenosarc. The cenosarc is the common body of the colony. New polyps grow on the coenosarc. Coenosarcs produce the coenosteum. The coenosteum is the colonyÕs exoskeleton. (Yao, 1995)
Longitudinal division is a common reproduction method. In longitudinal division, the coral polyp begins to broaden. It then divides into a coelenteron and mesenteries. Next, the mouth divides and tentacles encircle the new mouth. The difference between budding and longitudinal division is that during budding, the parent polyp produces a smaller polyp, whereas after division, the two polyps are identical. There is no distinction of parent and daughter polyps in a division. Individual polyps divide according to the radial arrangement of septa. Every new part has to complete its missing parts of the body and exoskeleton. While individual corals are able to reproduce by transversal division. Polyps and the exoskeleton divide transversally into two parts: basal and oral disc. The two new polyps must complete missing parts of the body and exoskeleton in order to function. (Yao, 1995)
Last method for coral colonies to propagate is through a process of fragmentation. A piece of colony can actually be broken off to grow a clone. Along with coral, starfish reproduce through fragmentation as well. Starfish are developmentally known as deuterostomes. Their embryo initially develops bilateral symmetry, indicating that starfish probably share a common ancestor with the chordates, which includes the fish. (Yao, 1995) Later development takes a very different path however as the developing starfish settles out of the zooplankton and develops the characteristic radial symmetry. Some species reproduce cooperatively, using environmental signals to coordinate the timing of gamete release; in other species, one to one pairing is the norm. While some starfish reproduce asexually by fragmentation, often with part of an arm becoming detached and eventually developing into an independent individual starfish. This has led to some notoriety. Starfish can be pests to fishermen who make their living on the capture of clams and other mollusks at sea as starfish prey on these. The fishermen would presumably kill the starfish by chopping them up and disposing of them at sea, ultimately leading to their increased numbers until the issue was better understood. A starfish arm can only regenerate into a whole new organism if some of the central ring of the starfish is part of the chopped off arm. (Yao, 1995)
From protozoa to pill bugs to porgies, changing from one sex to another is not just biological creativity, itÕs a way of life. It is also shocking proof that gender is much more versatile, flexible tool in Mother NatureÕs kit than anyone had previously realizedÑand kinkier than you ever imagined. The majority of reef fish change sex at some point throughout their life. In fact, reef fish that remain as the same sex for their lifespan are in the minority. There are many different patterns for sex-change. Some species will begin life as males and switch to females (protandry), and other switch from female to male (protogyny). For example, take the two-banded sea anemonefish. When another male anemonefish chances upon another male of the species, he starts to transform into a Ms. and invites the other fish to mate. Nobody get hurt and in time both pass their genes into the next generation. Perched in their anemone, they will live in monogamy until deaths do them apart. (Breder, 1996) On the other hand, I pity the poor female cleaner wrasse (Labroides dimidiatus) that has lived harmony with her sisters, protected and serviced by an iridescent male. One day, tragedy strikes and Mr. Wrasse vanishes. WhatÕs the girl to do? Be the man of course! As soon as the male is gone, the largest female in the harem begins to behave like a male: chasing girls, swaggering around, and being macho. Inside her ovary, often within 24 hours, the femaleÕs immune system is reabsorbing her eggs and turning on the testosterone. (Swearer, 1991) Within a week she (or rather he) will be producing viable, healthy sperm. (Swearer, 1991)
Further still, some will change sex in both directions, and others will be both sexes at the same time. Sex-change therefore becomes quite fascinating from several different perspectives. Although there is still much to learn about the endocrine system and the hormones that ÂÂdrive the process of changing sex. Also yet to be identified are the chromosomes and genetic sequences responsible for allowing the sexual plasticity.
Weird sex is all around us, in the ground beneath us, the air above our heads, and the sea from which we evolved. In fact, sex itself remains an unanswered biological mystery that has stumped scientists for decades. Since the 1960Õs, when traditional models of sex were scrapped (due to lack of evidence), evolutionary biologists have spawned great competing theories to explain why sex exists at all. But in this Darwinian scramble, one theoryÑThe Red QueenÑhas emerged in recent years to dominate them all. When looking at sexual dimorphism on the reef, there are a few factors to look at in animals: parental investment, intrasexual/intersexual competition, and female choice. Parental investment can be defined as the amount of resources by the parent to raise offspring at the detriment of the parentsÕ future reproductive efforts. (Yao, 1995) You would figure that the increased parental investment from females and lack of parental investment in males are inherent in male and female characteristics according to the Bateman Principle. (Breder, 1996) Prominent examples that have proven this to be false includes that of the pipefish where the males give more parental investment than the females and other fish that have one parent that guards the eggs and fry like bubble-nesters. (Breder, 1996)
While fish take some participation in parental investment, cephalopods invest no real care. Like other cephalopods, the Caribbean Reef Squid, is semelparous, dying after reproducing. Females lay their eggs then die immediately after. The males, however, can fertilize many females in a short period of time before they die. Females lay the eggs in well-protected areas scattered around the reefs. After competing with 2-5 other males, the largest male approaches the female and gently strokes her with his tentacles. At first she may indicate her alarm by flashing a distinct pattern, but the male soon calms her by blowing water at her and jetting gently away. He returns repeatedly until the female accepts him, however the pair may continue this dance or courting for up to an hour. The male then attaches a sticky packet of sperm to the female's body. As he reaches out with the sperm packet, he displays a pulsating pattern. The female places the packet in her seminal receptacle, finds appropriate places to lay her eggs in small clusters, and then dies. (Wood, 2008)
As squids die immediately after they lay their eggs or fertilize the eggs, octopi invest sometime in the eggs until they hatch. When octopuses reproduce, males use a specialized arm called a hectocotylus to insert spermatophores (packets of sperm) into the female's mantle cavity. (Wells, 1978) The hectocotylus in benthic octopuses is usually the third right arm. Males die within a few months after mating. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs are mature. After they have been fertilized, the female lays about 200,000 eggs (this figure dramatically varies between families, genera, species and also individuals). The female hangs these eggs in strings from the ceiling of her lair, or individually attaches them to the substratum depending on the species. The female cares for the eggs, guarding them against predators, and gently blowing currents of water over them so that they get enough oxygen. The female does not eat during the roughly one-month period spent taking care of the unhatched eggs. At around the time the eggs hatch, the mother dies and the young larval octopuses spend a period of time drifting in clouds of plankton, where they feed on copepods, larval crabs and larval starfish until they are ready to sink down to the bottom of the ocean, where the cycle repeats itself. In some deeper dwelling species, the young do not go through this period. This is a dangerous time for the larval octopuses; as they become part of the plankton cloud they are vulnerable to many plankton eaters. (Wells, 1978)
In the vertebrate family, all species of sharks, skates, and rays have what is called internal fertilization. Before the fertilization begins, the female releases a pheromone that dissolves into the water that allows males to home on the female that is ready to mate. The male then latches himself to the female via biting. The biting serves two purposes: foreplay and mate choice. In some species, like the sandtiger shark (Carcharias taurus) the females will bite back to discourage the advancing male if he is not to their liking. The sharks contain certain anatomical adaptations such as sexually dimorphic pelvic fins. The males have claspers that enter the femaleÕs cloaca during reproduction. The vas deferens (sperm duct) in male sharks opens into a syphon sac along the underbelly of the shark that is filled with sea water during copulation. The interesting thing is that the sperm is released into the syphon sac, probably hyper activated by the sea water (e.g. osmolarity, pH, etc.) and then pumped with the water from the syphon through the claspers into the female, where fertilization of the ovum (egg cell) occurs. However, some shark species, males will cooperate in raping females and thus get a chance to reproduce. This is the case for nurse sharks (Ginglymostoma cirraturm), where a group of males will rape uncooperative females. While some males block the females escape route, one will copulate with her.
Sexual reproduction helps individuals get ahead in this struggle, allowing creatures to mix their genes and produce hybrid offspring that might have a better chance for survival. Some say that males only exist for the reason of providing an extra genetic edge. From research this is a reason why sex exists at all, for females to be the target of male courtship behavior. In nature, however, social interactions rarely occur without other observers, thus, it is conceivable that some male courtship behaviors are directed not towards the female, but rather towards male rivals. Intersexual competition is competition for potential mates between members of the same sex. For example male Swordstail fish use their larger dorsal fin to scare off other males from the area. Intersexual competition involves members of both sexes of a species in their mutual pursuit rearing offspring. (Breder, 1996) Intersexual differs from intrasexual competition, because it usually involves female choice. Female Swordstail fish like males with smaller dorsal fins, therefore intrasexual selection outweighs intersexual competition. (Breder, 1996)
Although at the surface the ocean can appear calm and quiet, in fact there is an enormous amount of life activity taking place, particularly at certain times of the year. Reproductive strategies abound in the ocean where we have fission, budding, eggs hatching externally, eggs hatching internally, live births, some marine animals are born in freshwater, some are born on land, etc. The marine environment creates unique challenges to the cycle of life, some that have been met with amazing adaptability.
Bibliography
Bhamrah, H. S., Juneja, Kavita. (2002) A Textbook of Invertebrates. India: Anmol Publications.
Breder, Charles M, Rosen, Donn Eric. (1996) ÒModes of Reproduction in Fishes.Ó The American Museum of Natural History by The Natural History Press. Garden City, NY.
Fountain, Henry. (2007) ÒFemale Shark Reproduces Without Male DNA, Scientists say.Ó New York Times. 1 June, 2008. Hardy, Ian C. W. (2002) ÒSex Ratios Concepts and Research Methods.Ó NY: Cambridge University Press.
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Hansford, Dave. (2007) ÒMoonlight triggers coral ÔRomanceÕ.Ó National Geographical News.
Simpson, George G. (2003) ÒSimpson Rejected the Transformation From ÒDawn HorseÓ to Modern Horse?Ó Life of the Past. 28 May 2008.
Reinert, Birgit. (2002) ÒSex in the reef: How to tell coral species apart.Ó Genome News Network 28 May, 2008. < http://www.genomenewsnetwork.org/articles/06_02/sex_reef.shtml>.
Richmond, Robert. (1998) ÒCoral SpawningÓ. 28 May 2008.
Swearer, Stephen E., Warner, Robert R. (1991) ÒSocial Control of Sex Change in the Blueheaded Wrasse, Thalassoma bifasciatum (Pisces: Larbidae.Ó Biological Bulletin V181 (2). Marine Biological Laboratory.
Wood, Dr. James B. (2008) ÒThe Cephalopod Page.Ó 15 May 2008.
Wells, Martin John. (1978) ÒOctopus: physiology and behaviour of an advanced invertebrate.Ó New York: Halsted Press.
Yao, Zuxu, Crim, L.W. (1995) ÒCopulation, spawning and parental care in captive ocean poutÓ. Journal of Fish Biology. Canada: V. 47(1), 171-17.
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