Teleogryllus oceanicus

Teleogryllus oceanicus, commonly known as the Australian, Pacific or oceanic field cricket, is a cricket found across Oceania and in coastal Australia from Carnarvon in Western Australia and Rockhampton in north-east Queensland T. oceanicus populations in Hawaii arose through human-assisted introduction. It is currently unknown whether T. oceanicus was introduced to Hawaii in 1877 by area trade ships, or 1500 years ago with the original Polynesian settlers. Microsatellite comparisons support the idea that the Hawaiian T. oceanicus colonization originated in the Western islands and then spread East. T. oceanicus crickets are black to dark brown in coloration with longitudinal stripes on the back of the head. Males average between 28–35 mm in length, and the females are typically longer due to the ovipositor with an average of 33–42 mm. These crickets are typically found on soil ground hiding in fissures or holes in the terrain, and are typically only found in high numbers in landscapes that provide a good deal of cover. T. oceanicus may also be referred to as the black field cricket, a common name it shares with Teleogryllus commodus. The two species are nearly morphologically indistinguishable, the exception being that T. oceanicus males have a greater number of file teeth on their wings. T. oceanicus was originally regarded taxonomically as a geographic race of T. commodus, but was later recognized as a distinct species as growing evidence of reproductive isolation and differences in calling sound were reported. The two species' geographic ranges remain mostly separate with the exception of small overlap zones in Eastern Australia. There have been no reports of hybridization between the species in this overlap zone, thought to be due to differences in calling song acting as a pre-zygotic barrier. No character displacement has been observed in either species in this overlap region. Unlike T. commodus which lays eggs only a single time per season, T. oceanicus crickets breed year round. Like most cricket species, Teleogryllus oceanicus males produce a calling song to attract potential female mates. Crickets produce the sound of their calls using a 'file-scraper' system where, as the male opens and closes its wings, a plectrum (scraper) located on the posterior side of the left wing is rubbed against a filed vein located on the right wing. Structures called the harp and mirror allow the vibrations to resonate, producing the sound that we hear. Upon being approached by another individual, the male cricket will make antennal contact with the visitor. This contact allows a form of communication through chemoreception, and is important in determining the sex of the other individual. If the visitor is identified as a female, the male will begin the courtship behavior. During courtship, the male will begin singing the courtship song, which is much softer than the calling song, and is made of 7-10 amplitude-modulated chirps followed by a long and fast trill. As courtship progresses, the male will continue to stridulate and stroke the body of the female with his antennae. The female may respond by turning towards the male and contacting his abdomen with her forelegs, antennae and palpi. The male will then flatten his abdomen and spread his forewings, allowing the female to mount him, ultimately leading to copulation. During copulation, the male transfers his sperm to the female via spermatophore. After spermatophore transfer is complete, the male will attempt to remain in contact with the female to prevent her from removing the spermatophore. Unguarded female crickets have been shown to attempt to remove the spermatophore shortly after copulation. In crickets, male guarding behavior duration is closely related to the time it takes to complete sperm transfer. In crickets, it is the female sex that is choosy when responding to sexual signals. Sexual signals in Telogryllus oceanicus consists of multiple components. These components may be acoustic in nature, such as the calling song and the courtship song. Chemical components are also present in the form of cuticular hydrocarbons. In Teleogryllus oceanicus, the calling song is complex, consisting of a chirp made up of 4 similar pulses, followed by a trill of pairs of pulses. Properties of this calling song have been shown to vary with temperature. Because the calling song is species specific, and acts as a prezygotic mating barrier in Teleogryllus crickets, it is thought that the calling song is important for females to recognize same-species males. The male calling song also varies between populations. These differences are observed in total song length, pulse duration, and time between pulses. Females in all populations show a consistent preference for a higher proportion of the long chirp element. Because the long chirp element is more energetically demanding, this preference may serve as an honest indicator to the female in regards to the male's fitness.