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Gryllus bimaculatus

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Title: Gryllus bimaculatus  
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Subject: Crickets as pets, Wiki Ed/Saint Louis University/Evolutionary Biology, 3010-02 (Fall 2015), Polygamy, Ultrasound avoidance, Sexual conflict
Collection: Crickets, Gryllus, Polygamy
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Gryllus bimaculatus

Gryllus bimaculatus
Gryllus bimaculatus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Orthoptera
Suborder: Ensifera
Family: Gryllidae
Genus: Gryllus
Species: Gryllus bimaculatus
Binomial name
Gryllus bimaculatus
De Geer, 1773

Gryllus bimaculatus is one of many cricket species known as field crickets. Also known as the African or Mediterranean field cricket or as the two-spotted cricket, it can be discriminated from other Gryllus species by the two dot-like marks on the base of its wings.

The species is popular for use as a food source for insectivorous animals like spiders and reptiles kept as pets or in zoos. They are easy to raise and do not require prolonged exposure to cold in order to complete their life cycle.

Contents

  • Behavior 1
    • Fighting 1.1
    • Chirping 1.2
    • Shelter 1.3
    • Cannibalism 1.4
    • Circadian Rhythm 1.5
  • Breeding 2
    • Polyandry 2.1
    • Increased Genetic Diversity 2.2
    • Novel Mate 2.3
    • Sperm Competition 2.4
  • Economic importance 3
  • Polygamy 4
    • Polyandry 4.1
      • Sperm Competition 4.1.1
      • Male Guarding Behavior 4.1.2
  • References 5

Behavior

Fighting

In the wild, male crickets tolerate one another and will fight until there is a winner. The loser usually retreats without serious injury. The fighting method involves opening the mandibles as wide as possible, gripping onto the opponent's mandibles and pushing with the hind legs.

Chirping

Male crickets of this species produce several distinctive chirps, though each sound is made by rubbing the two outer wings together. Loud and steady chirps made throughout the night are to attract females and to warn off other males. Loud fast-frequency chirps are emitted when males encounter one another and are preparing to fight. They are intended to frighten off the rival male. A soft clipping sound is made when a female is known to be nearby. Its purpose is to encourage the female to mate.

Shelter

These crickets can be found hiding under logs, grasses, and in crevices. They can also dig holes into the ground to create homes for themselves, or live in holes created by other animals. Males are territorial and will fight off other males, but allow any number of females to coexist in the same shelter.

Cannibalism

Cannibalism is extremely rare, but females have been observed to eat males if there is not enough food to eat.

Circadian Rhythm

Pigment Dispersing Factor has been implicated in the nocturnal rhythms of crickets.[1]

Breeding

Females have a tubular organ at the rear, known as an ovipositor, which is used to lay eggs into the ground. They lay their eggs into humid soil and the baby crickets hatch in about two weeks.

Polyandry

Both sexes of Gryllus bimaculatus exhibit the sexual pattern of polyandry. Variation of polyandry occurs within populations of Gryllus bimaculatus between males and females. Like females, males continuously seek mates whom they can spread their seed. The rate of polyandry for males is unspecific but relatively high. An experiment on the species in Seville, Spain calculated through scientific processes such as genotyping, karyotyping, and allele counting, that female G. bimaculatus mate with at least two males before zygote production occurs.

Increased Genetic Diversity

This promiscuous mate selection is great for evolutionary progress. Polyandry is an evolutionary trait that directly increases genetic diversity which is a main contributor to evolution. The act of introducing more than one set of paternal alleles that can be present to a developing cell during zygote formation as a direct relation with genotypic and phenotypic variation.[2]

Novel Mate

Crickets of G. bimaculatus species demonstrate the Novel Mate hypothesis. The Novel Mate hypothesis states a female will avoid mating with males whom they have already done so. Evolutionary reasoning behind this process of sexual selection essentially boils down to an increase of genetic diversity. Rather, this differentiation between previous mates and novel ones allow females to search for genetically superior males which leads to more fit progeny.

Females are able to differentiate between novel and previous mates. Odor cues left behind by the female on the male are strong determinants. Before mating, palpation and antennation occurs, and key signals from these acts can lead the female to deduce whether or not a mate is novel.[3]

Sperm Competition

In polyandry, the amount of sperm ejaculated into the spermatophore directly relates with a males level of fitness and whether or not progeny from the female will exhibit his paternal genes. This level of fitness can be tested when other potential males are within close proximity.

The sperm competition theory which is true for G. bimaculatus states that there will be an increase in sperm expenditure when there is a higher risk of competition. Reproductive investment is metabolically straining; therefore, less desirable males invested more heavily in resources per reproductive opportunity when presented with a mate competitor in the environment.[4]

Economic importance

Gryllus bimaculatus is widely used by suppliers of live crickets for feeding to pet and zoo animals.[5]

Polygamy

Gryllus bimaculatus exhibit polygamy, in which one individual has many different mates. Polyandry is the most common form of polygamy practiced in G. bimaculatus.

Polyandry

Females show a distinct preference for mating with new males. Males do not show a difference in behavior when mating with a new female or an old mate. Males will show the same drive to mate with previous mates as with new mates.[6] The ability of a male cricket’s sperm to successfully fertilize a female’s egg after mating varies depending on various traits, which includes the amount of sperm that is effectively delivered through mating.[7] The more sperm that is deposited results in greater fertilization success because more eggs are able to hatch.[8] The order in which various males mate with one female before fertilization also affects fertilization success. The last male that mates with a female tends to have the highest fertilization success.[9] Other traits that affect fertilization success relate to the physical characteristics of sperm itself. Traits that increase the ability of a male’s sperm to successfully fertilize a female’s egg compared to that of another male are most advantageous. This is because these traits have been selected for over traits that have lower fertilization success.[10]

Polyandry is a costly reproductive system, but it still evolved in crickets because it provided benefits. It allows females to mate with males that have more desirable traits than previous mates. It produces more genetic variation in the population because new combinations of genes are able to come together through this multiple mate system. It also allows females to avoid mating with infertile males. Two mechanisms that allow polyandry to be advantageous despite its costs are sperm competition and male guarding behavior.[11]

Sperm Competition

Sperm competition is the interaction between sperm traits and female selection of these traits. It allows males with more advantageous traits to survive and reproduce more than less fit males.[12] Sperm competition also helps to prevent genetically unsuited individuals from mating. Inbreeding is a major example of genetic incompatibility because more genetically related individuals tend to have offspring with lower fitness. As a result, male crickets that are genetically similar to female mates tend to be less effective in producing offspring because they are not selected as mates as often as genetically dissimilar males.[13]

Male Guarding Behavior

Male guarding behaviors are when male crickets guard female crickets after recently mating with them. These behaviors protect the guarding male’s sperm and allow this sperm to fertilize the female’s egg, despite the increase in predation of the guarding male. As a result, the guarding male’s advantageous traits are passed on. Male guarding behaviors also reduce the risk of females becoming prey. When males protect female mates from predators, these females are saved from death. This not only has the benefit of allowing that particular male’s sperm to become fertilized, but also allows the female to continue to survive and reproduce. This in turn can lead to increased mating between the female and guarding male.[14]

References

  1. ^ Hassaneen E, El-Din Sallam A, Abo-Ghalia A, Moriyama Y, Karpova SG, Abdelsalam S, Matsushima A, Shimohigashi Y, Tomioka K (26 February 2011). "Pigment-dispersing factor affects nocturnal activity rhythms, photic entrainment, and the free-running period of the circadian clock in the cricket gryllus bimaculatus". Journal of Biological Rhythms 1: 3–13.  
  2. ^ Bretman, A., & Tregenza, T. (2005). Measuring polyandry in wild populations: a case study using promiscuous crickets. Molecular Ecology, 14(7), 2169-2179.
  3. ^ Bateman, P. W. (1998). Mate preference for novel partners in the cricket Gryllus bimaculatus. Ecological Entomology, 23(4), 473-475.
  4. ^ Mallard, S. T., & Barnard, C. (2003). Competition, fluctuating asymmetry and sperm transfer in male gryllid crickets (Gryllus bimaculatus and Gryllodes sigillatus). Behavioral Ecology and Sociobiology, 53(3), 190-197.
  5. ^ "Crickets". The Amphibian. Retrieved 17 May 2015. 
  6. ^ Bateman, Philip W. (1998-11-01). "Mate preference for novel partners in the cricket Gryllus bimaculatus". Ecological Entomology 23 (4): 473–475.  
  7. ^ "Saint Louis University Libraries | Saint Louis University". apps.webofknowledge.com.ezp.slu.edu. Retrieved 2015-10-21. 
  8. ^ "Saint Louis University Libraries | Saint Louis University" (PDF). www.jstor.org.ezp.slu.edu. Retrieved 2015-10-21. 
  9. ^ "Saint Louis University Libraries | Saint Louis University". apps.webofknowledge.com.ezp.slu.edu. Retrieved 2015-10-21. 
  10. ^ Snook, Rhonda R. (2005-01-01). "Sperm in competition: not playing by the numbers". Trends in Ecology & Evolution 20 (1): 46–53.  
  11. ^ Bateman, Philip W. (1998-11-01). "Mate preference for novel partners in the cricket Gryllus bimaculatus". Ecological Entomology 23 (4): 473–475.  
  12. ^ Snook, Rhonda R. (2005-01-01). "Sperm in competition: not playing by the numbers". Trends in Ecology & Evolution 20 (1): 46–53.  
  13. ^ "Saint Louis University Libraries | Saint Louis University" (PDF). www.jstor.org.ezp.slu.edu. Retrieved 2015-10-21. 
  14. ^ Rodríguez-Muñoz, Rolando; Bretman, Amanda; Tregenza, Tom (2011-10-25). "Guarding Males Protect Females from Predation in a Wild Insect". Current Biology 21 (20): 1716–1719.  
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