Philippines is an archipelagic area comprised of islands that encloses marine areas that serves as a habitat to marine fauna. Its terrestrial flora and fauna and marine fauna are highly diverse as a result of the construction of the islands. The process which formed these islands together also made the seas around these islands. Ergo, flora and fauna in the older islands are more endemic than those of new islands formed. Flora may be difficult to be reproduced in another island if this specific flora is not eaten either by human or transporting animals that could transfer seeds from place to place. Moreover, mollusks endemic to a certain area are only found in there because larva of these mollusks could hardly swim from a marine area to another and different species of mollusks need different depth of water habitat. This isolation results to diversity and endemicity of Philippine flora and fauna.
This premise is very feasible and accountable. Philippines is indeed a place abundant of diverse organisms. It is true to the fact that these islands that comprise the archipelago made the country bountiful of various species that are also endemic as well. The formation of these islands is mainly the amazing factor that resulted to this archipelagic beauty.
Differences in spawning time, mate recognition, environmental tolerance, and gamete compatibility have been all implicated in marine speciation events (Palumbi, 1994). Speciation is an adaptive process which involves intrinsic barriers to gene flow between closely related populations by development of reproductive isolating mechanisms (Bush, 1975). Reproductive barriers which involve the initial reduction of gene flow between populations and some evolutionary forces that produced these barriers may be a problem in speciation (Coyne & Orr, 2004). Speciation is characterized by gene separation and morphological differentiation (Stearns, & Hoekstra, 2000).
Geographic isolation may be the cause of speciation in the Philippines (UCMP, 2006). The location of the species may prevent them to interbreed with another type if for instance they were secluded in another place. This diversity within the Philippine archipelago is a result of the collision of Australian plate with the Eurasian plate (Whitmore, 1981 as cited by Vallejo). Speciation is more likely to occur in isolated islands and would result to higher levels of endemicity of species.
Philippines is a crucial hotspot for both terrestrial and aquatic biodiversity and endemicity because of its geographic and geologic history of the islands. The most isolated islands have the highest number of endemic plants and animals (Heaney, 1986, as cited by Vallejo). In this case, Philippines is an archipelagic area that allows biodiversity and endemicity to arise. To quote Oosterzee, 1997, “The Philippines is, therefore, an elegant natural experiment in speciation.
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Among the diverse marine species in the Philippine setting, Tridacna gigas, is the largest bivalve mollusk and is capable of reaching 4 feet (1.2 meters) in length and weighing more than 500 pounds (227 kg). Its average life span in the wild is 100 years or more. This marine giant lives in the warm waters of the South Pacific and Indian Oceans. It consumes the sugars and proteins produced by the billions of algae that live in its tissues. The giant clam uses a siphon to draw in water to filter and consume passing plankton.
Giant clams reproduce sexually through broadcast spawning. These mollusks expel sperm and eggs into the sea. Fertilization takes place in the open water and is followed by larval stage. The larvae must swim and feed in the water column until they are sufficiently developed to settle on a suitable substrate and begin their adult life as a sessile clam. These giant clams are said to be killers for they are suspected of trapping people and drowning them. Tridacna species are lethargic and closes slowly, only when it is disturbed, which negates the accusation.
The adductor muscle of Tridacna gigas is considered a delicacy of some people and overharvesting it for food, shells and the aquarium trade has led it on to be listed by the International Union for Conservation of Nature as a vulnerable species.
References:
Bush, G.L., (1975). Modes of animal speciation. Retrieved on September 21, 2010 from http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.es.06.110175.002011
Coyne, J. A., & Orr, H. A., (2004). “The problem of speciation”, in Speciation.
Heaney, L. R., (1998) as cited by Vallejo, (2005). The biogeography of philippine marine mollusks.
National Geographic (2010). Giant Clam. Retrieved on September 23, 2010 from http://animals.nationalgeographic.com/animals/invertebrates/giant-clam.html
Oosterzee, P. v., (1997) as cited by Vallejo, (2005). The biogeography of philippine marine mollusks.
Palumbi, S.R., (1994). Genetic divergence, reproductive isolation, and marine speciation. Retrieved on September 21, 2010 from http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.es.25.110194.002555
Stearns, S. C., & Hoekstra, R. F. (2000). Evolution: an introduction.
Tervo, K. and R. Csomos (2001).Tridacna gigas. Animal Diversity Web. Retrieved on September 23, 2010 from http://animaldiversity.ummz.umich.edu/site/accounts/information/Tridacna_gigas.html.
The University of California Museum of Paleontology (2006). Modes of speciation. Retrieved on August 15 2009 from http://evolution.berkeley.edu/evosite/evo101/VCCausesSpeciation.shtml
Whitmore, T. C., (1981) as cited by Vallejo, (2005). The biogeography of philippine marine mollusks.
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