Christmas Island Whiptail Skink: The Yellow Crazy Ant and the Skinks Approach to Reproduction - Research Paper Example

Ecological Context of the Christmas Island Whiptail Skink The intention in this paper is to explore the ecological context of the Christmas Island Whiptail Skink. More specifically, emphasis will focus on two primary aspects of that ecology. The first is the ecological implications of its primary enemy, the Yellow Crazy Ant, and the negative impact of humans. The second is the ecological implications of the skink’s approach to reproduction. This paper will present the situation and its implications, and will argue that there is strong correspondence among the factors involved. Christmas Island is in the Eastern Indian Ocean, south of Indonesia, and is part of the Christmas and Cocos Islands tropical forests eco-region (Christmas Island, ND). It is located at precisely 10°305 105°40E; 134 km2) (Drake, Bodey, Russell, D.R. Towns, & Ruffino, 2011). The island belongs to Australia, which fact has resulted in an ecological nightmare for that nation. This topic is, therefore, a timely and significant one. About 60 million years ago, a volcano rose above the surface of the sea. An atoll of coral formed around it and this resulted in limestone deposits. About 20 million years ago, this volcanic mountain began to sink into the sea, and the coral had to work hard to deposit enough limestone to stay in shallow water. Then, about 10 million years ago, three uplift incidents occurred, resulting in the limestone capped mountain being divided into three terraces. Today the island is 361 meters above sea level, covered in vegetation and rainforest, isolated and surrounded by deep water (Pavils, 2011). The raised reefs on the highest portion of the island were noted, 125 years ago, to be the highest ones known in the world (Lister, January 1888) Humans first settled on Christmas Island 120 years ago (Gilligan, 2011). In 1899, phosphate mining destroyed some of the rainforest and poisoned the marine environment, as well, leaving roads and mining sites as scars on the primeval earth, and damaging coral in the sea (Gilligan, 2011). In 1980, a National Park was established (Pavils, 2011). The island was nearly used for a Russian-Asian space program, but was saved by an environmental assessment that scared off investors, fortunately (Pavils, 2011). Now, more than 60% of Christmas Island is under the protection of the Environment Protection and Biodiversity Conservation Act 1999 (Australian Government Department of Sustainability, Environment, Water, Population, and Communities, 2002) The Christmas Island Whiptail Skink, shown below, is a species of endemic reptile that lives in this bio-diverse island, along with other endemic reptiles: the Christmas Island Blind Snake, Lister’s Gecko, the Blue-tailed Snake-eyed Skink, and Sadleir’s Bow-fingered Gecko (Christmas Island, ND) and one native reptile species, Emoia Atrocostata, all of which, except the still common Sadleir’s Bow-fingered Gecko, are nearing extinction (Smith, et al., 2012). The Christmas Island Whiptail Skink prefers to be in forest clearings, on fallen leaves, on low plants and ground cover, tree buttresses, and in the sunlight that sneaks through the rainforest cover (Cogger, 2010). Its scientific name is Emoia nativitatis, from the phylum of Iachorda, class of Reptilia, and family of Scincidae (ZipcodeZoo.com, 2012). A name used synonymously, for this tiny (6.2 cm) skink is Lygosoma nativitatis (International Union for Conservation of Nature and Natural Resources, 2012). Here is a map showing the distribution of the Christmas Island Whiptail Skink on the Island (Macdonald, 2013): The Christmas Island Whiptail Skink is critically endangered. That label was determined, due to it being found in an area of less than 100 square kilometers, on Christmas Island only, and its drastically declining habitat and population (International Union for Conservation of Nature and Natural Resources, 2012). The main factor for this has been identified as the Yellow Crazy Ant, (International Union for Conservation of Nature and Natural Resources, 2012) whose official name is Anoplolepis gracilipes (Stewart, Brown, Richards, & Bernard, 2012). In fact, its population has decreased by 98%, due to the invasion of Christmas Island by Yellow Crazy Ants (Rawson, 2012), which the World Conservation Union refers to as “one of the worlds worst invasive creatures” (Roberts, 2007). They arrived by cargo ship, between 1915 and 1934 (Gilligan, 2011), probably from Hawaii (Basavaraju, Chakravarthy, Doddabasappa, & B. Nagachaitanya, 2010) or elsewhere. They kill by spraying formic acid on their prey. This leaves their prey blind and paralyzed, causing it to die of dehydration and starvation (Roberts, 2007). Here is a photo of the Yellow Crazy Ant (Lowe, Browne, & Boudjelas, 2000) Photo: H. T. Imai and M. Kubota The ants are not merely enemies of the Christmas Island Whiptail Skink, but also kill off huge populations of Red Crabs, 20-30 million of them, as a matter of fact (Roberts, 2007). The Yellow Crazy Ant is not native to Christmas Island, having arrived there, by accident, in the early 1900s and reproduced so rapidly that they were a very serious problem by the late 1990s (Roberts, 2007). Furthermore, while the Yellow Crazy Ant lives in other parts of the world, the Christmas Island Whiptail Skink lives only on Christmas Island, and nowhere else. The ants combine forces with each other and form huge super-colonies, with hundreds of queens present , and they can double their population each year (Roberts, 2007). They expand their claimed territory at an alarming rate. They also farm scale insects for their sticky honeydew. The honeydew gets on the trees and causes a mold to grow, which destroys the tree (Roberts, 2007). Furthermore, because the Red Crabs have been destroyed by the Yellow Crazy Ants, the balance of animals and insects and vegetation has been thrown off. For example, with insufficient crabs to exert control, the population of poisonous centipedes has grown astronomically, and these centipedes attack the Christmas Island Whiptail Skink at night, when they are trying to get some rest (Low, October 2009). Also, because the ants destroy Red Crabs, and these crabs control vegetation balance, now weeds have taken over and the Christmas Island Whiptail Skink has a less desirable habitat, even aside from the direct threats posed by the acid-spraying ants (Roberts, 2007) and the poisonous centipedes. At one time, the Australian government felt confident about their efforts to control or eradicate the ants, but time has proven that to be an overly-optimistic attitude. They spread poisonous bait by hand and, when that was problematic, they sprayed fipronil insecticide out of a helicopter (Gilligan, 2011). David Kemp, federal environment minister in 2003, prematurely declared the eradication campaign to be a success, and the Parks Department was issued the Banksia Foundation Award that year, but the situation only worsened (Roberts, 2007). In Spring 2007, the five leading scientists, running the eradication effort, resigned to protest the government’s insufficient funding of their efforts, and the Australian Government quickly pumped more money into the eradication program (Roberts, 2007). The Yellow Crazy Ants have continued to spiral Christmas Island ecology out of control, and are directly or indirectly responsible for the dangerous decline in Flying Foxes, the Pipistrelle Bat, Coconut Crabs, and seabirds, among other Christmas Island wildlife and the Christmas Island Whiptail Skink (Roberts, 2007). However, research from South Africa indicates that boric acid is far more effective and environmentally friendly than fipronil insecticide, at controlling Yellow Crazy Ants. It drove the ants out of all Christmas Island test areas for nine months, although the ants increased their populations and expanded their territory in the untreated areas (Stewart, Brown, Richards, & Bernard, 2012). Perhaps this research has come in time and will prove to be the answer, and perhaps it will not, or may not be funded even if it is promising. The Queensland government has currently given up on the Yellow Crazy Ant eradication effort, believing it to be a waste of money and priorities, because the ant seems to be ineradicable. Instead they have funded the eradication of wild dogs on the mainland, since that is politically supported by grazers (Booth, 2012). This does not bode well for the Christmas Island Whiptail Skink. In addition to the Yellow Crazy Ant, humans also have a detrimental ecological impact. This paper has earlier noted the history of phosphate mining. Farming and settlements have further claimed land on Christmas Island. The 400 million dollar Christmas Island Detention Centre, built in 2006 to house 400 detainees, has expanded to include tent facilities for hundreds more, and also has a staff of 300 personnel who fly in and out regularly, causing additional ecological challenges. The detention centre destroyed a large chunk of rainforest in the northwest of the island (Gilligan, 2011). The distribution map, included in this paper, shows that this was also a habitat area for the Christmas Island Whiptail Skink. It was also the very last habitat for the Pipistrelle Bat, now basically extinct (Gilligan, 2011). The Yellow Crazy Ant’s detrimental impact on the biodiversity of Christmas Island is not simply a horror story confined to one little remote island. World ecology is comprised of the inter-relationship of smaller balanced ecosystems, so the loss of biodiversity in one island actually impacts the ecology of the entire planet. Furthermore, the Yellow Crazy Ant has rapidly spread to various parts of the world, where it is causing trouble for other ecosystems. Researchers in India estimate that 80% of endangered species, in the world, will be the competitive loser or be preyed upon by invasive species (Basavaraju, Chakravarthy, Doddabasappa, & B. Nagachaitanya, 2010). The invasive species can weaken other species by hybridizing and instigating genetic pollution, which can lead to extinction of the weaker species (Basavaraju, Chakravarthy, Doddabasappa, & B. Nagachaitanya, 2010). They can change the function of an eco-system. The effects of human habitation (clearing land), can put pressure on the local plants, animals and insects, making them more vulnerable to an invasive species (Basavaraju, Chakravarthy, Doddabasappa, & B. Nagachaitanya, 2010). This has clearly happened to the Christmas Island Whiptail Skink, and that is why it is now critically endangered. Crazy Ants also can interfere with reptile reproduction in the forest (Lowe, Browne, & Boudjelas, 2000). The Christmas Island Whiptail Skink is oviparous, which means that it reproduces by laying eggs (Macdonald, 2013). To keep eggs safe requires camouflage, and for the skink, that camouflage is leaf litter and other ground vegetation. Unfortunately, due to the impact of the Yellow Crazy Ant, in claiming territory for super-colonies, farming scale insects for honeydew (resulting in tree mold and tree loss), and killing off the Red Crabs (who processed the leaf litter, managed seedlings, and kept weeds away), and with forest being claimed by humans for an asylum-seeker detention centre, farming, and phosphate mining, the Christmas Island Whiptail Skink has lost a lot of forest, leaf litter, and low vegetation that can shelter their eggs. The Christmas Island Whiptail Skink has also been displaced from various places that were natural habitats. Change of habitat can possibly influence skink gender (Young, 2009). This could have further ecological impact, as well. There is fascinating research indicating that skinks have various ways, at their disposal, for gender selecting offspring (Young, 2009). As in humans and most other animals, gender, in skinks, is determined by chromosomes. An XX combination yields a girl and an XY combination yields a boy. Skink gender, however, can be the result of variation in temperature and yolk size, as well (Young, 2009). Richard Shine’s research group, at University of Sydney, found that if a skink egg is incubated at a low temperature, even an XX chromosome combination will yield a male (Young, 2009). At low temperature, it was found also that small yolk size yielded a male and large yolk size a female. In fact, when Radder (Shine’s colleague) removed yolk from the eggs, this yielded 88% males, while adding yolk to eggs yielded 93% females (Young, 2009). He found many XX males and XY females, in analyzing the results (Young, 2009). On Christmas Island, given the ecological disaster it has become, there is no shortage of altered variables which might reasonably impact the temperature and yolk size of the Whiptail Skink’s eggs. It might be speculated that as the Yellow Crazy Ants damage the forest canopy, directly and indirectly, and the leaf litter processing, seedlings, and low vegetation are made less hospitable by the drastic decline in Red Crabs, the Whiptail Skink may have to lay its eggs in nests that are less hidden, more highly warmed by the sun, and this could possibly result in significantly more females being born. Alternatively, they may, in a desperate attempt to escape the ants, head for the higher elevation volcanic hills, and this could also result in a change in usual nest temperature, and thus in altered gender allocation. Fipronil insecticide, used in Christmas Island ant eradication efforts, has been found to be toxic to reptiles, so the skink may be damaged by it. One research study found that administration of fipronil-contaminated food, to lizards, resulted in a 62.5% death or dying rate within four weeks. Those lizards which survived this treatment ate significantly less food, lost significant body weight and organ-to-body weight ratios (Preveling & Demba, July 2003). This demonstrated fipronil’s high toxicity to lizards. Research justifies the use of birds as a surrogate species, in assessing chemical risk to lizards, since there is insufficient data on lizards and since birds have been found to be even more sensitive to toxic chemicals than reptiles (Weir, Suski, & Salice, December 2010). A Swiss study on insecticides, including fipronil, tested in Africa to evaluate efforts to eradicate or control locusts and tsetse flies, found residue in the livers of reptiles, and found that birds and reptiles are the most sensitive wildlife to chemical toxins (Peveling & Nagel, 2001). It is, therefore, interesting that a research study found that fipronil is passed from the Zebra Finch mother to the egg, causing failure to hatch, severe developmental delay in the survivors (14% survived), and fipronil found in liver, brain, and other tissues (Kitulagodage, Buttemer, & Astheimer, 2011). Fipronil injected into the egg yolk sac of domestic chickens resulted in developmental delay, behavior abnormality, reduced feeding, reduced weight, and fipronil residue in brain and liver (Kitulagodage, Buttemer, & Astheimer, 2011). There is, therefore, some basis for concern for the effects of fipronil on the health, mortality, and well-being of the Christmas Island Whiptail Skink. Eradication efforts, or even habitat displacement, might possibly leave the skinks vulnerable to less robust yolks, and this could conceivably result in a surplus of males. A surplus of males could mean less reproductive outcome, and could easily lead to extinction. It might also lead to hybridization with a non-critically endangered reptile, which could lead to gene pollution and extinction. It is also possible that a surplus of females could lead to eventual hybridization and consequent gene pollution, infertility (as with some hybrids), and extinction. Alternatively, it may not be unreasonable to wonder if, like the New Mexico Whiptail Lizard, and some other reptile species (the Komodo Dragon and the Rattlesnake, for example), the Christmas Island Whiptail Skink might turn to parthenogenesis, in case of a female gender surplus. Parthenogenesis (reproducing without fertilization by the male) has been documented in 70 species around the world, but is still relatively rare. There are two types of parthenogenesis: obligate and facultative. Obligate is when asexual reproduction is normal and usual for a species, while facultative is when asexual reproduction occurs in response to the absence of a suitable male (Watts & al., 2006). Speculation about the possible eventual parthenogenesis response to a female surplus would specifically refer to facultative parthenogenesis. No one can yet predict the long-term outcomes of the impact of Christmas Island’s ecological disaster situation, on the Christmas Island Whiptail Skink, nor how the skink adapts or fails to adapt to the circumstances. Ubiquitous in the literature is the emphasis on how complex are the factors involved on all sides of this disaster, and how they are not yet fully identified or understood. Research-informed speculation, then, also has a role to play, to reflect on what these factors might be and how they might interact, to motivate public interest, research and eradication or control funding. 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