Reproductive interference, the phenomenon at the heart of this observation, refers to sexual behavior between individuals of different species during mate acquisition that results in a loss of fitness for one or both species. Researchers distinguish several types along a temporal continuum, ranging from disruption of sexual communication signals to late-acting processes such as successful copulation and hybridization. The boundaries between these types are gradual, and many species pairs display more than one. Heterospecific copulations occur when premating barriers between species are absent or inadequate, or when one sex—usually the female—is unable to reject forced copulations from a heterospecific partner. When such copulations do take place, postmating barriers hinder the production of hybrids, and the fitness costs are the highest of any stage of reproductive interference, because gametes, energy, and nutrients are wasted on offspring that will never be viable.

What makes the Slovak observation so exceptional is that hybridization between closely related grasshopper species has been documented under field conditions only indirectly, primarily through molecular genetic analyses revealing gene flow. Studies have shown gene flow between the Californian species Melanoplus sanguinipes and M. devastator, and between the European grasshoppers Chorthippus montanus and C. parallelus. Successful hybridization is confirmed by the appearance of hybrid individuals in a population, but most interspecific copulation attempts do not result in viable offspring. Direct observations of heterospecific mating in the field are anecdotal, with only one case previously reported for any Orthoptera species. Mating between representatives of different higher taxonomic categories, such as genera, is even less likely to be witnessed. In grasshoppers, sexual interactions between species usually occur through acoustic interference—males of one species disrupting the songs of another. But the two Slovak species cannot stridulate at all, which changes the dynamics entirely.

Both the green mountain grasshopper and Nagy’s mountain grasshopper are mute, unable to produce sound because of their very short forewings. Both live in mountains, preferably in grassland habitats between 600 and 1550 meters above sea level. They belong to different taxonomic subtribes within the tribe Podismini—Miramellina and Podismina, respectively—but their close phylogenetic relationship suggests a shared evolutionary origin. European Podismini taxa are estimated to have diverged from their Asian counterparts approximately 38 million years ago. Both species are less common in the Western Carpathians of Slovakia and are rare in Poland, Czechia, and Hungary. Crucially, they occur locally syntopically—living side by side in the same sites—but, as far as records show, only in Slovakia. In two species that do not stridulate, heterospecific mating attempts or erroneous female choice are therefore more likely than in acoustically signaling pairs, because one of the usual barriers to cross-species sexual communication simply does not exist.

The field survey that produced the observation was part of an orthopterological study of the Veľká Fatra range. The site, a subalpine grassland on carbonate soils with a southeastern aspect, held up to 30 adults per 100 square meters of each species, making both the most abundant of the 20 Orthoptera taxa recorded there. During the three-hour survey, no other heterospecific copulating pair was found, while conspecific copulations were regularly observed in both species. No individuals with an obvious hybrid phenotype were seen at the site. The researchers photographed the pair in copula—both individuals, remarkably, were hosts of velvet mites of the genus Trombidium—and then transported the copulating pair to the laboratory for closer study.

In the insectary, kept at 24 degrees Celsius on a 16-hour light and 8-hour dark cycle, the pair copulated at least twice more during the 54 days both individuals remained alive. During that time, the female laid two egg pods. The researchers investigated the embryonic developmental stage of the collected eggs by dissecting a single specimen of the preserved clutch under a stereo zoom microscope. The lipid yolk pieces in the dissected egg showed considerable differences in size, a pattern usually observed when a fertilized egg enters the early stages of embryogenesis. This suggests that the egg may have been fertilized, although the evidence stops short of confirming viable hybrid offspring.

To confirm the identity of the parental specimens, the team turned to genetics. DNA was extracted from the hind femur muscle tissue of adult specimens and from the whole eggs using a high-salt protocol. Partial sequences of the internal transcribed spacer 1, or ITS1, region were amplified to confirm the identity of the parental specimens. The PCR amplification used specific primers and carefully controlled thermal cycling conditions, with products purified and sequenced using the Sanger method. In total, four P. nagyi and five M. alpina individuals were successfully genotyped, including the female M. alpina from the copulating pair. The genetic analysis confirmed the species identity of both parents. Unfortunately, it was not possible to obtain a sufficient amount of DNA from the eggs for sequencing, so the question of whether the eggs were true hybrids remains open. The DNA sequences were deposited in the NCBI database under accession numbers PQ654838 through PQ654846, with PQ654838 corresponding to the female from the copulating pair.

The observation is consistent with evidence that the green mountain grasshopper and Nagy’s mountain grasshopper are more closely related to each other than to other species within their respective subtribes. Analyses of nuclear and mitochondrial DNA fragments reject the monophyly of Eurasian Podismini subtribes, which had previously been proposed based on either morphological or cytological features. The evolutionary proximity of parental species facilitates hybridization, because close relatives are more likely to be genetically compatible and can therefore produce viable offspring. In particular, the shape of the genitalia, which is used to distinguish Pseudopodisma from Miramella, does not appear to prevent copulation between the two genera. This finding supports the hypothesis that the two species are closely related and suggests the need for a taxonomic revision within the tribe Podismini. The researchers also note that the question remains whether copulation is possible in the reverse position—a female P. nagyi with a male M. alpina.

The syntopic occurrence of the two species in the Western Carpathians is relatively rare, even though they favor the same type of mountain grassland habitats. Of 31 sites where both species co-occur, the shared sites represent 14 percent of all recorded M. alpina sites and 35 percent of P. nagyi sites across five Western Carpathian mountain ranges in Slovakia: Veľká Fatra, Nízke Tatry, Vysoké Tatry, Poľana, and Veporské vrchy. This pattern can be explained by reproductive interference, which can reduce population viability wherever the two species are in contact. If heterospecific mating occurs more often than the single documented instance, it may impact the viability of populations of both the green mountain grasshopper and Nagy’s mountain grasshopper wherever they are in contact. Further data are needed to test whether reproductive interference reduces the viability of their syntopic populations.

To gain deeper insight into the evolutionary consequences of heterospecific hybridization between these taxa, it would be necessary to collect a range of hybrid specimens at different stages of development—something that has not yet been achieved. For now, the single copulating pair from Ostredok stands as one of the very few direct field observations of mating between grasshopper genera anywhere in the world. It reminds researchers that species boundaries, even between genera, can be more porous than taxonomy suggests, and that in the quiet mountains of Slovakia, two mute grasshoppers may be quietly rewriting the evolutionary history of their lineage. Whether their encounter was an evolutionary accident or the first sign of a deeper overlap between two lineages on the brink of revision, only further fieldwork and genetics will tell.

Subject of Research: Heterogeneric mating between two Podismini grasshopper species ( Orthoptera , Acrididae , Melanoplinae )

Article Title: Heterogeneric mating between two Podismini grasshopper species ( Orthoptera , Acrididae , Melanoplinae )

Article References: Jarčuška, B., Búci, M., & Krištín, A. (2026). Heterogeneric mating between two Podismini grasshopper species (Orthoptera, Acrididae, Melanoplinae). Journal of Orthoptera Research, 35(1), 167-170. https://doi.org/10.3897/jor.35.169103

Image Credits: AI Generated

DOI: 10.3897/jor.35.169103

Keywords: Heterogeneric, mating, between, Podismini, grasshopper, species, Orthoptera, Acrididae, Melanoplinae, scientific research