Metrodorini

Cadena-Castañeda, Oscar J., Quintana-Arias, Ronald Fernando, Infante, Ivette Coque, Silva, Daniela Santos Martins & Tavares, Gustavo Costa, 2025, Studies on pygmy grasshoppers: On the current Metrodorinae sensu lato classification (Orthoptera: Tetrigidae) with emphasis on American and Malagasy taxa, Zootaxa 5597 (1), pp. 1-265 : 244-245

The tribe Metrodorini and its subtribes

This tribe was recently delimited by Kasalo et al. (2023a), who synonymized the tribes Miriatrini and Mucrotettigini under Metrodorini . Here, these tribes are proposed as subtribes that are well differentiated according to what is provided in the diagnoses and keys. When verifying these characteristics, it is evident that the head characters tend to be similar to those of Metrodorina stat. nov. and Mucrotettigina stat. nov., but other characters, such as the number of antennal segments and pronotal characters, are useful in separating these taxa and not keeping a tribe with many genera without providing a more comprehensive and ordered organization.

It is evident that knowledge about the taxonomy of Tetrigidae has been incipient. For a long time, there were no contributions from much of the world, mainly from America. At the beginning of this century and its second decade, there was not enough information as we have today. Very few people have taken on the task of contributing to the Tetrigidae family and other taxa. Moreover, it is worth mentioning Silva et al. (2019a) that, even not having a complete picture at that time of the classification of Mucrotettigini (although similar to some metrodorines), preferred to keep it within Cladonotinae , while the taxonomy of the subfamilies was refined since almost all the genera were originally described as cladonotines by Perez-Gelabert et al. (1998). Therefore, the decision of Silva et al. 2019a should not be considered a “failure”, as mentioned by Kasalo et al. (2023a); the tribes that Silva et al. (2019) described only remained within the subfamily Cladonotinae awaiting future contributions. In the same way that other authors did, it is important to avoid making drastic changes without a complete picture or enough evidence. For instance, Adžic et al. (2020) preferred to keep the tribes Thoradontini and Criotettigini outside of Scelimeninae ( Tetrigidae ). This position is valid and conservative and seeks to reduce noise in the classification. Still, if the status of Thoradontini and Criotettigini is resolved in the future, it would not be correct to mention that the authors “failed” to exclude those tribes from the subfamily in which they traditionally grouped once they followed the information and evidence available at the time.

Mucrotettigina stat. nov. groups the Antillean metrodorine taxa, although very similar to Metrodorina stat. nov. (most continental taxa). Mucrotettigina stat. nov. is only represented by wingless species—although they had winged ancestors, such as † Electrotettix , the wings disappear in the descendants. This subtribe apparently had rapid radiation, somewhat more significant than that of the continental taxa, and maybe a different clade than the two continental subtribes ( Heads, 2009; Heads et al., 2014; Silva et al., 2019a).

Kasalo et al. (2023a) proposed keeping Eleleus Bolívar, 1887 within Cladonotinae (without tribal assignment) due to the non-development of the vertex carinae, in contrast to the other genera with which it was previously associated. Nevertheless, the development of the vertex carinae can be variable, very conspicuous like Miriatra , or moderate like Metrodora . However, Hottettix has an organization of the vertex carinae similar to Eleleus , which would conflict with the proposal of Kasalo et al. (2023a). Additionally, Eleleus curtus has the first and third segments of the hind tarsus of subequal lengths ( Pavón-Gonzalo et al., 2012). Unfortunately, there are no additional specimens in better condition of E. curtus Bolívar, 1887. Until this change, little progress can be made in the placement of this taxon, which could be a Metrodorinae , since Cladonotinae from continental America has not been reliably recorded.

Metrodorina stat. nov. includes most taxa of continental metrodorines. This contribution provides a similar taxonomic treatment as the Antillean taxa of Mucrotettigina stat. nov., which resulted in the division and description of additional genera. Now, Metrodorina stat. nov. groups eight genera in contrast to eleven recent ones of Mucrotettigina stat. nov. (not counting the two fossil genera), being the greatest generic diversity in the insular region. Unlike the insular ones, the continental subtribes tend to have greater numbers of antenomeres. This character has proven to be useful in differentiating the subtribes, and it also varies in some subfamilies, so it should be integrated as much as possible into the descriptions of new taxa and redescriptions of others. Metrodorina stat. nov. is widely distributed from southern Brazil to Nicaragua, the known species tend to be robust, wingless, and with little capacity for dispersion, so surely the number of taxa currently known must be more significant since several distributional gaps persist.

Miriatrina stat. nov., the second and least diverse of the continental subtribes, contains three genera with seven species, mainly Amazonian and with one species present in the Andes of Colombia. This taxon has gone through several configurations. First, it was a tribe that grouped the majority of Metrodorinae s. l. with pronounced fastigium ( Cadena-Castañeda & Cardona-Granda, 2015). Later, it was proposed as a monogeneric tribe ( Silva et al., 2017), and finally, it was synonymized by Kasalo et al. (2023a). Here, it is proposed as a well-differentiated subtribe within Metrodorini , the only one with winged taxa of the tribe, which, although having a prolonged fastigium, fulfills the diagnostic characteristics of the tribe, in terms of the organization and development of the carinae of the vertex.

The tribe Metrodorini is the most diverse and rich group of Metrodorinae s. str., likewise the one with the broadest distribution and the only one with a presence on the continent and in the Antilles. This is curious since almost all of them are wingless, and the disappearance of wings has occurred independently multiple times, and winged species remaining rare. Possibly, the dispersion of the tribe occurred since ancient times, and it is possible Antillean colonization could have happened in a similar way as has been indicated for the tribe Otteiini ( Phalangopsidae ), which has a similar distribution of island taxa from Central America ( Cadena-Castañeda et al., 2021c). This contrasts with the Kasalo et al. (2023a) hypothesis, which suggested the colonization occurred via South America, citing Iturralde-Vinent & MacPhee (1999). Still, the proposal of these authors works for the origin and distribution of taxa from the Lesser Antilles, which did emerge from South America, unlike the Greater Antilles, which originated in another way ( Pindell, 1994; Gordon et al., 1997; Iturralde-Vinent, 2004). Therefore, the proposal by Kasalo et al. (2023a) is probably not feasible since there is no presence of Metrodorini in the Lesser Antilles, and they were actually referring to the colonization of the current distribution of island taxa, which are between Cuba and Hispaniola.