Morphological ant mimics: constrained to imperfection?

Adaptive evolution relies on both heritable variation and selection. Variation is the raw material upon which selection acts, so any mechanism that limits or prevents the generation of heritable variation reduces the power of selection to lead to adaptation. Such limitations are termed evolutionary constraints. While it is widely accepted that constraints play an important role in shaping evolutionary outcomes, their relative importance, as opposed to adaptation, in determining evolutionary outcomes remains a subject of debate. Evolutionary constraints are often evoked as the reason behind the persistence of inaccurate mimicry. Here, we compared the variation and accuracy of body-shape mimicry in ant-mimicking spiders with that of ant-mimicking insects, predicting greater constraints, and hence inaccuracy, in spiders mimicking ants, due to their evolutionary distance from the ant model. We found high inter-species variation in mimetic accuracy, but dorsally, no overall difference in mimetic accuracy between spider and insect mimics, which is inconsistent with a constraint causing inaccurate mimicry. Our study provides empirical evidence suggesting that imperfect mimicry in spiders and insects is predominantly shaped by adaptive processes rather than constraints or chance. Our findings contribute to our understanding of the mechanisms underlying evolutionary diversity and the processes that shape phenotypic outcomes.

Increased speed of movement reduced identification of Batesian ant-mimicking spiders by surrogate predators.

In Batesian mimicry, the mimic gains protection from predators by imitating a noxious model. Some myrmecomorphic species use ants as models as ants have strong defensive capabilities. Ants are highly mobile models, and besides colour, shape, and size, mimics also imitate their movement. Yet, former studies focused mainly on static traits. Here, I tested the hypothesis that artificially increased speed of movement reduces the probability of the mimic being identified. First, images of 14 myrmecomorphic spider species and their models were used for humans to rank their mimetic accuracy. Humans were used as surrogate predators to obtain scores for each mimetic pair. In the second experiment, the effect of movement playback speed on the probability of identification was investigated, again using humans. Videos of mimics were played at different speeds, and the identification probability was recorded. While ants were correctly identified at any playback speed, the identification of myrmecomorphic spiders declined with increasing playback speed. In other words, the latency to correct identification increased with playback speed. Overall, mimics with higher accuracy scores were more difficult to identify while moving. The natural speed of movement of accurate mimics was similar to that of inaccurate ones. Movement is thus an important trait for myrmecomorphic species.

Transformational Mimicry in a Myrmecomorphic Spider.

Species that are Batesian mimics during postembryonic development shift between mimetic models as they grow in size. However, it has not yet been tested whether these successive mimetic phenotypes are similarly protected from predators. Early-instar phenotypes could represent an inaccurate phenotype or an accurate phenotype because of selection from different predators. Here, we tested the hypotheses of transformational Batesian mimicry in the ant-mimicking jumping spider Leptochestes berolinensis. We quantified the mimetic accuracy of different ontogenetic stages to potential ant models by using a multitrait approach. We measured movement, body profile, body size, and coloration. Analysis revealed adults to be more accurate mimics than juveniles. Adults were similar to smaller morphs of Camponotus or Lasius ants, whereas juveniles were more similar to Lasius and Colobopsis ants. We tested whether predators, mantises, and Pisaura spiders were deceived by mimics after having experience with ant models. These predators never captured any ant or a mimic but always captured the nonmyrmecomorphic spider. We conclude that L. berolinensis is a Batesian mimic of ants undergoing transformational mimicry, with all stages being accurate mimics.

The superficial ant: a revision of the Neotropical ant-mimicking spider genus Myrmecium Latreille, 1824 (Araneae, Corinnidae, Castianeirinae).

The ant-mimiking spider genus Myrmecium Latreille, 1824 is revised, including 38 species, all herein diagnosed, described and illustrated. The following synonymies are proposed: Myrmecium aurantiacum Mello-Leitão, 1941 syn. nov. with M. camponotoides Mello-Leitão, 1932; M. gounellei Simon, 1896 syn. nov. and M. obscurum Keyserling, 1891 syn. nov. with M. latreillei Lucas, 1857; M. itatiaiae Mello-Leitão, 1932 syn. nov. and M. vertebratum Walckenaer, 1837 syn. nov. with M. rufum Latreille, 1824. Myrmecium bonaerense Holmberg, 1881 is considered as species inquirenda. Males of M. dacetoniforme, Mello-Leitão, 1932, M. fuscum Dahl, 1907, M. latreillei Lucas, 1857, M. trifasciatum Caporiacco, 1947 and adults of M. viehmeyeri Dahl, 1907 and M. reticulatum Dahl, 1907 are described for the first time. Myrmecium bifasciatum Taczanowski, 1874, M. monacanthum Simon, 1897 and M. rufum Latreille, 1824 are also redescribed and illustrated. The following 28 new species are described, diagnosed and illustrated: M. amphora sp. nov. (female from Chichiriviche, Venezuela); M. bolivari sp. nov. (male and female from Caracas and Sucre, Venezuela and Colombia); M. carajas sp. nov. (male from Pará, Brazil); M. carvalhoi sp. nov. (female from Piauí, Tocantins and Goiás, Brazil); M. catuxy sp. nov. (female from Amazonas, Brazil and Puerto Lopez, Colombia); M. chikish sp. nov. (female from Huánuco, Peru); M. cizauskasi sp. nov. (male and female from Amazonas, Brazil); M. oliveirai sp. nov. (male from Amazonas, Brazil); M. deladanta sp. nov. (male from Sucúmbios, Ecuador); M. diasi sp. nov. (male and female from Amazonas, Brazil); M. erici sp. nov. (female from British Guiana); M. ferro sp. nov. (female from Paraiba, Brazil); M. indicatti sp. nov. (male and female from Pará, Brazil); M. nogueirai sp. nov. (female from Amazonas, Brazil and Madre de Dios, Peru); M. lomanhungae sp. nov. (male and female from Amazonas and Pará, Brazil); M. machetero sp. nov. (female from Beni, Bolivia); M. malleum sp. nov. (male and female from Aragua and Lara, Venezuela and Caldas, Colombia); M. oompaloompa sp. nov. (male and female from Bahia, Brazil and Kurupukari, Guyana); M. otti sp. nov. (male and female from Pará, Amazonas and Mato Grosso, Brazil and Madre de Dios in Peru); M. pakpaka sp. nov. (male and female from Huánuco, Peru); M. raveni sp. nov. (male and female from Amazonas and Pará, Brazil); M. ricettii sp. nov. (male and female from the states of Pará, Alagoas, Sergipe, Bahia, Goiás and Mato Grosso, Brazil and Puerto Lopez, Colombia); M. luepa sp. nov. (male from Bolívar, Venezuela); M. souzai sp. nov. (male from Amazonas, Brazil); M. tanguro sp. nov. (male and female from Rondonia, Mato Grosso, Brazil); M. tikuna sp. nov. (male from Amazonas, Brazil); M. urucu sp. nov. (female from Amazonas, Brazil); M. yamamotoi sp. nov. (male and female from Amapá, Amazonas and Pará, Brazil and Marowijne, Suriname).

The role of ultraviolet colour in the assessment of mimetic accuracy between Batesian mimics and their models: a case study using ant-mimicking spiders.

The use of ultraviolet (UV) cues for intra- and inter-specific communication is common in many animal species. Still, the role of UV signals under some predator-prey contexts, such as Batesian mimicry, is not clear. Batesian mimicry is a defensive strategy by which a palatable species (the mimic) resembles an unpalatable or noxious species (the model) to avoid predation. This strategy has evolved independently in many different taxa that are predated by species capable of UV perception. Moreover, there is considerable variation in how accurately Batesian mimics resemble their models across species. Our aim was to investigate how UV colour contributed to mimetic accuracy using several ant-mimicking spider species as a case study. We measured the reflectance spectrum (300-700 nm) for several species of mimics and models, and we tested whether they differ in visible and UV colour. We modelled whether two different predators could discriminate between mimics and models using colour information. We found that generally, ant-mimicking spiders differed significantly from their ant models in UV colour and that information from the visible range of light cannot be extrapolated into the UV. Our modelling suggested that wasps should be able to discriminate between mimics and models combining information from visible and the UV light, whereas birds may not discriminate between them. Thus, we show that UV colour can influence mimic accuracy and we discuss its potential role in Batesian mimicry. We conclude that colour, especially in the UV range, should be taken into account when measuring mimetic accuracy.

Trait-mediated indirect interactions of ant shape on the attack of caterpillars and fruits.

Mainly owing to their high diversity and abundance, ants are formidable as predators and defenders of foliage. Consequently, ants can exclude both invertebrate and vertebrate activity on plants via direct and indirect interactions as already shown in many previous studies. Here we present empirical evidence that objects resembling ant shape on dummy caterpillars were able to repel visually oriented predators. Moreover, we also show that rubber ants on dummy fruits can repel potential fruit dispersers. Our results have direct implications on the ecological and evolutionary dynamics of interactions in ant-based systems, as ant presence could affect the fitness of its partners. In short, our study highlights the importance of visual cues in interspecific interactions and opens a new way to study the effects of ant presence to test ecological and evolutionary hypotheses.

A new species of the genus Castoponera (Araneae, Corinnidae) from Sarawak, Borneo, with comparison to a related species.

A new species of the genus Castoponera Deeleman-Reinhold, 2001, Castoponera christae sp. n., is described here. The species is closely related to Castoponera lecythus Deeleman-Reinhold, 2001, but can be distinguished by the structures of the male palp and the female genitalia.