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HERMIT CRABS.
Term Paper ID:30074
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Essay Subject:
Discusses different kinds of Hermit Crabs, their habitats and their characteristics.... More...
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5 Pages / 1125 Words
4 sources, 7 Citations,
APA Format
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Paper Abstract:
Discusses different kinds of Hermit Crabs, their habitats and their characteristics. Usefullness in research. Series of activities of Hermit Crabs value for research into decision-making. Importance of shells and skill selection behavior. Ability of researchers to observe the assessment procedure of the crabs. Variouis experiments on Hermit Crabs in reference to animal behavior; response to stimuli.
Paper Introduction:
Hermit crabs usually are found in empty gastropod shells, seeking protection from predators, desiccation, and other hermit crabs. The hermit crab does not seem to select a place to stay at random but rather appears to have a selection process. Precisely what this process is and how the crab makes a decision as to what shell to select and what shell to reject is the subject of much research.
Hermit crabs are crustaceans that live in the wild in the western Atlantic. They mate on land near the sea, and once the eggs develop, the female carries the eggs on her abdomen to the sea and leaves them on wet sand or a wet rock for the tide to carry out to sea. There are usually 1,000 to 50,000 eggs at a time. At sea, the crabs are small larvae that molt several times in order to grow to adulthood. At the adult larvae stage,
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"Effects of shell and foodavailability on metamorphosis in the hermit crabs Pagarus hirsutiusculus(Dana) and Pagarus granosimanus (Stimpson)." Journal of ExperimentalMarine Biology and Ecology 25, 237-249. Mesce, K.A. Researchhas found that a number of different elements may be involved or thatdifferent species of hermit crab may respond to different stimuli. Conover (1978) reports on a study on shell selection by the hermitcrab, using the Pagurus pollicaris in a natural population and inlaboratory experiments. (1978). It is not enough simply todemonstrate the existence of a pattern and a potential process. The crabs were collected in Tampa Bay south of St.Petersburg, Florida. Theauthors examine the combined effects of shell and food availability on thesurvival of the megalopal stage and on the duration of this stage in thetwo species noted. Various comparisons were made between shells as to size,weight, amount of epifauna, and so on. Mesce (1993) examines the shell selection behavior of two closelyrelated hermit crabs, Pagarus samuelis and Pagarus hirsutiusculus. In the wild, hermit crabs canlive up to 25 or 3 years. The authors assume that adultbehavior reflects the importance of shells to postlarval fitness and thatmegalopal delay capabilities are regulated by requirements at thepostlarval stage, and they then predict that Pagarus granosimanus is morelikely to delay metamorphosis than Pagarus hirsutiusculus. This meansthat underlying sensory and other neural mechanisms make it possible ofreach species to detect and respond quickly to the type of shell it prefers(Mesce, 1993, 659-671). When an animal stops performing oneactivity, it must decide what activity to perform next; this is called a"decision point." At any given time, causal factors for several differentpotential activities are likely to be present, and the question arises asto how the animal selects which activity to perform. Hermit crabs are prime candidates for thecomparative approach because adult and juvenile crabs have immediate andessential requirements for a limited resource, namely empty shells to beused as housing. They are nocturnal. "The shell selection behavior of two closelyrelated hermit crabs." Animal Behavior41, 659-671. The hermitcrab does not seem to select a place to stay at random but rather appearsto have a selection process. A betterapproach is suggested by framing the hypothesis as a comparative statementof testable predictions. Thefirst acquires new shells two to four times more quickly than the secondand can evict Pagarus hirsutiusculus from high quality shells. They also have an extensive repertoire of behaviorsmaking it easier to locate, assess, and retain suitable shells. This suggests that shell volume is more important than weight inthe selection of a shell. (1993). When the weight of the shell wasincreased by 25 percent or so either by its natural epifauna orartificially, hermit crabs continued to occupy shells of the same size andvolume. Other experiments shifted the angle of the shellaxis and position of the shell's center of gravity, which often resulted inan aversion to the altered shells by hermit crabs. Theygrow on land by shedding their exoskeleton. Hermit crabs are crustaceans that live in the wild in the westernAtlantic. Elwood, R.W. Assessments and decisions.London: Chapman and Hall. References Conover, M.R. This suggested that thecrabs select shells on the basis of several shell traits bearing onprotection provided by the shell or by the ease with which the shell can becarried (Conover, 1978, 131-142). This series of activities seems to be theprocess of information gathering and decision making for the crab (Elwoodand Neil, 1992, 53). Hermit crabs are known to contest the ownership of shells, andmany of the resource assessment procedures seen in a fight are similar tothose used in selecting empty shells (Elwood and Neil, 1992, 25). Eachspecies showed a different preference for either Tegula funebralis shells(in the case of P. Both types of crab responded to the chemicalcomposition of the shells, especially to the calcium content, and theapplication of various coatings was tried to remove the calcium from thecover of the shell. It is suggested on the basis of information about adultbehavior that Pagarus granosimanus is more focused on finding, assessing,and retaining high quality shells than is Pagarus hirsutiusculus. An excess of shells was available in this areabecause only 53 percent of the available shells were occupied by hermitcrabs because of the population ratio. Adultexamples of Pagarus hirsutiusculus, and especially the males, have atendency toward reduced shell living and often occupy shells that do notcompletely cover the vulnerable abdomen. These shells differ greatly in their external appearanceand their internal configuration. "The importance of various shellcharacteristics to the shell-selection behavior of hermit crabs." Journalof Experimental Marine Biology and Ecology 11, 131-142. Harvey, A.W. Harvey and Colasurdo (1993) examine the effects of shell and foodavailability on the process of change in two species of hermit crab, thePagarus hirsutiusculus and Pagarus granosimanus. Few studies have addressed the selective disadvantagethat might cause a delay in metamorphosis. There are usually1, to 5 , eggs at a time. and Colasurdo, E.A. The larvae stage of manyspecies of marine invertebrates delay their metamorphosis until they detectparticular cues. The crab musthave an optimal shell, and the crab typically engages in a series ofactivities ending when he either rejects a shell or moves out of the oldshell and into the new one. The delaycapabilities of Pagarus granosimanus, however, are relatively trivialcompared to other invertebrates (Harvey and Colasurdo, 1993, 237-249). (1993). It is believed thatshells are more important for Pagarus granosimanus. The researcher can alter the shells so they conveydifferent information to the animal, after which the consequences can bedetermined. Records were kept of all collectedgastropod shells as to species and whether or not they were inhabited by ahermit crab. At the adult larvaestage, the hermit crabs begin looking for a shell to live in, and once itfinds a suitable shell, it lives on land for the rest of its life. Hermit crabs usually are found in empty gastropod shells, seekingprotection from predators, desiccation, and other hermit crabs. In most animals,assessments can only be inferred based on the decisions the animals make,but with hermit crabs the assessment procedure itself can be observed andthe sequence of investigatory acts can be recorded and the timing ofdecisions noted. The hermit crab is ideal for this type of research because theshells selected by the crab can be changed in a number of ways for purposesof experimentation and because the behavior is so predictable. Once this cue was removed, Pagarus hirsutiusculusalone did not begin shell exploratory behavior. and Neil, S.J. At sea, the crabs are small larvae thatmolt several times in order to grow to adulthood. They mate on land near the sea, and once the eggs develop, thefemale carries the eggs on her abdomen to the sea and leaves them on wetsand or a wet rock for the tide to carry out to sea. Pagarus hirsutiusculus, on the other hand, did not showthis tracking behavior. Precisely what this process is and how thecrab makes a decision as to what shell to select and what shell to rejectis the subject of much research. Both species reliedheavily on the chemical cues in order to locate and uncover shells thatwere partially buried, and it seems that both species rely on shell cuesthat are distinguishing features of the shells they prefer. samuelis) or Nucella canaliculata shells (for P.hirsutiusculus). Shells are an important resource for the hermit crab. The various experiments on hermit crabs show the variety of elementsthat have to be considered when trying to ascertain the reasons for animalbehavior and the way researchers can manipulate these elements in order tochange behavior and demonstrate a relationship between a stimulus and aresponse. Hermit crabs are considered ideal forresearch into decision-making. Pagarus samuelis relied on visual cuesfor shell selection, and this species also displays visually-mediatedtracking of objects resembling the shell of choice in terms of color,shape, and size. It was foundthat the behavior of Pagarus granosimanus is affected by the availabilityof food and by whether or not the crab has a shell. (1992). Hermit crabs are scavengers with a strong senseof smell.
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