Cherax

Members of the cherax genus can be found in lakes, rivers, and streams across most of Australia and New Guinea.[1]

The most common and widely distributed species in Australia is the common yabby (C. destructor). It is generally found in lowland rivers and streams, lakes, swamps, and impoundments at low to medium altitude, largely within the Murray–Darling Basin. Common yabbies are found in many ephemeral waterways, and can survive dry conditions for long periods of time (at least several years) by aestivating (lying dormant) in burrows sunk deep into muddy creek and swamp beds.

In New Guinea, Cherax crayfish are found widely in rivers, streams, and lakes, with a particularly high diversity in the Paniai Lakes.[2] New Guinea is also home to the only known cave-living crayfish in the Southern Hemisphere, C. acherontis.[3]

They are opportunistic and omnivorous feeders. Their diet includes plants, algae, macrophytes, snails, insects, and tadpoles. Cherax grip live food in their large front claws and when the prey is no longer moving, they pass it along to their smaller claws that sit right below their mouths and pick apart small pieces to place in their mouths.[6]

The mating season for Cherax is during early spring. After fertilisation, eggs develop inside the mother’s body for 4 to 6 weeks. After that period, the eggs transition to the outside of the mother's body and rest on the female’s tail. Then the eggs continue to develop and hatch in spring.

Both sexes of Cherax are selective with copulation partners. Females tend to choose males with a larger central mass (abdomen and tail) and cheliped. Males tend to select copulation partners who have larger body sizes and are virgins. Opposed to females who were more dominant or had symmetrical chelipeds.[7]

As part of a mating/copulation, ritual males and females fight each other. This allows the female to test the strength of the male to determine if they will produce profitable offspring.[8] During the fight both release urine. The female’s release of urine triggers a sexual response from the male.[8] The male's release of urine is an aggressive response towards the fight with the female. When the male smells the female's urine it will stop releasing its own, hoping the female will allow them to copulate.

Once the female has allowed the male to deposit its sperm. The male will position itself on its back and deposit its sperm.[9] Unlike other crayfish species, the Cherax dispar does not use its cheliped to cage females during copulation. It is mainly used during mating when the males and females fight.

The slender crayfish (Cherax dispar) is one of many animals that resolve conflicts with displays of strength without the need to participate in physical combat allowing them the opportunity to benefit from dishonest signalling regarding strength. Both sexes of Cherax dispar (C. dispar) utilise their chelae when intimidating or engaging in agonistic encounters with rivals.[10] C. dispar uses either dishonest or honest signalling depending upon whether they are male or female.

Studies have found that male C. dispar uses dishonest signalling of strength through their enlarged front claws, termed chelae, which they use in threatening displays to their competitors.[10] Males engage in chelae displays to indicate dominance prior to engaging in violent contact and such displays are capable of completely de-escalating an altercation over 80% of the time.[10] In males, larger chelae result in greater dominance; however, the actual strength of one’s chelae does not influence an individual’s dominance as a result of dishonest signalling.[10] In instances when displaying males have chelae of a similar size, they will engage in combat and those with the greater chelae closing force will win.[11]

Female C. dispar uses honest signalling of strength meaning the size of their chelae is a good indication to other C. dispar about that individual's strength.[11] Individuals possessing larger chelae engage in more agonistic encounters and are also more likely to win.[11] In a study of female C. dispar chelae strength, they found that chelae size also indirectly indicated the dominance of the female because of its honest indication of strength.[11]

In a study of functional trade-offs of chelae size, experimenters found that enlarged chelae negatively correlated to escape swimming performance in males but not in female C. dispar.[12] Therefore, indicating that large chelae in males could act as a handicap if they needed to escape from a competitor or predator.[12] The chelae muscles of male slender crayfish produce only half of the force that female chelae muscles are capable of producing, indicating that males invest more resources into developing larger chelae for intimidation purposes than they do for producing functioning chelae muscle.[10] Between unfamiliar opponents, chelae closing force determines the winner of agonistic encounters; however, the recognition of individuals and their fighting abilities amongst slender crayfish that previously engaged in fights will influence who wins in future encounters.[13] This mechanism reduces the number of physical encounters a single individual will have to engage in.[13] Male C. dispar has a clear cost-benefit relationship as a result of using dishonest signalling. The costs include decreased escape, increased predation, and increased need for resources in order to grow the enlarged chelae. While the male C. dispar benefits from its ability to win more conflicts without having to expend excess energy by engaging in a physical conflict.

Cherax boesemani

The genus contains 59 species:[3][14]