In a remarkable discovery in Thailand’s Khao Yai National Park, a team of researchers from Kasetsart University, led by Narin Chomphunut, unearthed a rare bilateral gynandromorph spider of the species Tidarren sisyphoides. This unique specimen, exhibiting male characteristics on its left side and female traits on its right, is the first of its kind documented in the country. The details of this find were published in the Journal of Arachnology.
The Discovery Process
On July 15, 2023, during a routine biodiversity survey in Khao Yai National Park, Narin Chomphunut and her team stumbled upon this unusual spider. The specimen was found near a forest trail while the team was collecting samples. An initial visual inspection revealed asymmetrical genitalia, a characteristic that immediately caught the team’s attention and prompted them to document the spider through photographs and careful capture.
The spider was then transported to Kasetsart University’s entomology lab in Bangkok for a more detailed examination. Here, genetic testing confirmed the spider’s gynandromorphic condition, making it a significant find in the field of arachnology.
Characteristics of the Gynandromorph Spider
The Tidarren sisyphoides specimen exhibits a fascinating split in its physical traits. The left side of the spider, with a body length of 4.2 mm, displays male characteristics such as an embolus on the pedipalp and a darker coloration typical of males. This side of the spider also has a smaller body, another common trait in male spiders.
Contrastingly, the right side of the spider shows female features. It has a larger body length of 7.8 mm, an epigyne for egg deposition, and a lighter, broader abdominal patterning. The spider’s bilateral split allows it to engage in limited mating behaviors, although the viability for reproduction remains uncertain.
The Species Tidarren sisyphoides
The Tidarren sisyphoides, also known as the “ballooning spider,” is a native of Southeast Asia and belongs to the family Theridiidae. Females of this species typically measure between 6-9 mm, while males are smaller, measuring between 3-5 mm. Males of this species are known for their unique emasculation ritual during mating, where they sever their own genitals to avoid being eaten by females.
In Thailand, the species is commonly found in lowland forests like Khao Yai National Park. Here, they prey on small insects using their irregular webs, contributing to the park’s diverse arachnid population.
Understanding Gynandromorphism in Arachnids
Gynandromorphism is a condition that occurs due to genetic anomalies during embryonic development. It results in organisms exhibiting both male and female physical traits, as seen in this spider’s 50/50 bilateral division. In spiders, such cases are extremely rare. Prior to this discovery, only about 20 such cases had been documented worldwide, mostly in orb-weavers rather than theridiids.
Interestingly, the condition does not appear to affect the spider’s web-building or predatory abilities. Observations in the lab showed that the gynandromorph spider was able to function similarly to its non-gynandromorph counterparts.
Location and Habitat Details
Khao Yai National Park, where the spider was found, is located 150 km northeast of Bangkok in Nakhon Ratchasima Province. The park spans 2,168 square kilometers and is a UNESCO World Heritage site known for its diverse arachnid populations. The specific location of the find was at coordinates 14°25’N 101°22’E, in a humid understory area with dense vegetation at an elevation of 300 meters.
Thailand’s tropical climate, characterized by average temperatures of 28°C and high humidity, provides an ideal environment for the proliferation of Tidarren sisyphoides in forested habitats like these.
Scientific Implications and Research
This discovery has significant implications for the study of genetic variations in Thai arachnids. It has prompted Kasetsart University to expand surveys across 10 additional national parks in the country. Narin Chomphunut, the lead researcher, stated, “This gynandromorph challenges our understanding of sex determination in spiders and could inform studies on sexual dimorphism.”
The study also recommends further genomic sequencing of the specimen to identify the exact chromosomal anomaly responsible for the bilateral split. This could provide valuable insights into the genetic mechanisms underlying gynandromorphism, potentially advancing our understanding of this rare condition in arachnids.