Menemerus tropicus

Menemerus tropicus is a species of jumping spider in the genus Menemerus that lives in Kenya and Uganda near Lake Victoria. The spider lives in large nest complexes that can stretch between trees in mangrove savannas. The species was first described in 2007 by Wanda Wesołowska, one of over 500 descriptions she has written during her lifetime. It is a small spider, with a flattened cephalothorax that is between 1.7 and 2.1 mm and a rounded abdomen between 1.7 and 2.9 mm long. The female is larger than the male and has a darker abdomen and lighter carapace. The male abdomen has a pattern that includes a brown streak and silver spots. The female has a yellowish streak, in some examples, with yellow patches. The legs are brown and yellow. The copulatory organs help distinguish the species from others in the genus. The male has a very short double embolus and very large retrolateral apophysis. The female has a narrower pocket in its epigyne, narrow insemination ducts and small spherical spermathecae.

Taxonomy
Menemerus tropicus is a species of jumping spider that was first described by Wanda Wesołowska in 2007. It was one of over 500 species identified by the Polish arachnologist during her career, making her one of the most prolific experts in the field. She allocated the spider to the genus Menemerus, first circumscribed in 1868 by Eugène Simon. It contains over 60 species. The genus name derives from two Greek words, meaning certainly and diurnal. The genus shares some characteristics with the genera Hypaeus and Pellenes.

Genetic analysis has shown that the genus is related to the genera Helvetia and Phintella. The genus was placed in the tribe Heliophaninae, which was renamed Chrysillini by Wayne Maddison in 2015. The tribe is ubiquitous across most of the continents of the world. It is allocated to the subclade Saltafresia in the clade Salticoida. Chrysillines are monophyletic. In 2016, Prószyński created a group of genera named Menemerines after the genus. The vast majority of the species in Menemerines are members of the genus, with additional examples from Kima and Leptorchestes. The species name recalls the tropical climate where the spider lives.

Description
Menemerus tropicus is a small spider. The male has a low flattened cephalothorax that is between 1.7 and 2.0 mm long and between 1.3 and 1.6 mm wide. The carapace is dark brown, covered in dense brown and grey hairs. A band formed of white hairs line the sides of the carapace. It has a darker eye field, almost black with long brown bristles near the eyes themselves. The spider has a low dark clypeus that features a scattering of grey hairs. The chelicerae, labium, maxilae and sternum are brown. The abdomen is between 1.7 and 2.2 mm long and between 1.4 and 1.7 mm wide. It is rounded and flattened with a pattern consisting of an irregular brown streak down the middle, scattered with silver spots, and brown patches on the sides. It is covered in dense brown and grey hairs like the carapace, which are longer to the edges. The underside is greyish. It has beige spinnerets. The front legs are brown, the remainder yellow with brown patches, all with brown spines and hairs. The pedipalp is brownish, although the cymbium is darker. The spider has an elongated palpal bulb that has a very short double embolus with a tegular apophysis that curves with it into the bulb. There are two appendages, or apophyses, on the tibia. The retrolateral tibial apophysis is large and bulbous. The ventral apophysis on the top of the tibia is very small and spiky.

The female is larger than the male. It has a cephalothorax that is between 2.0 and 2.1 mm long and 1.5 and 1.6 mm wide and an abdomen that is between 2.4 and 2.9 mm long and 1.8 and 2.2 mm wide. It is generally similar to the male but clothed with dark hairs rather than grey and brown hairs. The carapace is lighter but the abdomen is darker. The abdomen also has a distinctive pattern with a yellowish streak down the middle that, in some examples, is complemented by two lines of yellow patches. The underside is dark grey. The chelicerae are brown like the male but female labium and maxilae have pale yellow chewing margins that do not exist on the other sex. The spinnerets are dark. The legs and pedipalps are yellow with brown patches. The spider's epigyne has a large central depression, sometimes partially plugged by wax, and a notch on the very rear. The copulatory ducts lead to narrow insemination ducts, with long accessory glands leading to the end of the ducts, and small spherical spermathecae.

Spiders of the Menemerus genus are difficult to distinguish. The copulatory organs enable the species to be identified. The female is similar to the related Menemerus paradoxus, but has a narrower pocket in its epigyne and smaller spermathecae. The male has similarities to Menemerus meridionalis but differs in having a larger retrolateral apophysis.

Behaviour
Like many jumping spiders, Menemerus spiders do not spin webs to capture prey. Instead, they are mainly diurnal hunters that use their good eyesight to spot their prey. The spiders transmit vibratory signals through silk to communicate to other spiders and use visual displays during courtship. The males will undertake a zigzag dance and quiver their pedipalps before the female. They form groups in loose association with each other. They are hesitant attacking other spiders but the males undertake aggressive displays between themselves. They are also known to embrace, usually holding on for between 1 and 5 seconds.

Distribution and habitat
Menemerus spiders are found throughout Africa and Asia, and have been identified as far as Latin America. Menemerus tropicus is found in Kenya and Uganda. The male holotype was found at Mbita Point, Kenya, on the side of Lake Victoria at an altitude of 1150 m above sea level in 2001. It has subsequently been found in Homa Bay and Nakuru. The first examples to be found in Uganda were discovered in 1996 in Entebbe, also on the lake. Others have subsequently found in the same area.

The species lives in mangrove savanna near freshwater. It seems to particularly thrive amongst trees of the Combretaceae family. The spider lives in large nest complexes that contain many different species. Sometimes, the spiders will create webs that stretch between different plants to create very large complexes. Each spider has its own nest within the complex, generally spaced between 5 and 15 mm, but also occasionally touching.