The South Western Mediterranean is an extraordinary area of diversification of plants and animals with confluence of species or populations with similar habitats on both sides of the Ibero-Maghrebian region. The connexion of both continents in Late Miocene (Messinian stage: 7,2-5,3 MYa) increased dispersion and the diversification and vicariance phenomena of the biota in a complex scenario while climate changes also multiplied ecological successions (Blondel & Aronson, 1999) and biodiversity (Sanmartín, 2003; Hidalgo-Galiana & Ribera, 2011). This area forms part of one of the main hot spots of biodiversity of the planet (Myers et al., 2000). The Mediterranean biomes are among the most threatened regions in the world and predictions point to consider the Western Mediterranean as especially vulnerable to biodiversity loss due to drastic changes in human land use and global climate change (Giorgi & Lionello, 2008; Klausmeyer & Shaw, 2009).

Among the extraordinary biodiversity of this region, a good example of North African influence in SW Europe is the presence of singular cricket species of the genus Sciobia Burmeister, 1838. This genus constitutes a peculiar group of cricket taxa that originated and radiated from North of Africa, some of which colonised SW Europe. There are 37 Sciobia species described to date (Eades et al., 2016) four of which occur in the Iberian Peninsula (see reviews in Gorochov & Llorente, 2001; Barranco & Aguirre-Segura, 2013). Two species of Sciobia, subgenus Thilptoblemus, inhabit a relatively small piece of land in Europe, in the SW of the Iberian Peninsula. These two species are easily recognized by sight and morphology (i.e. Barranco & Aguirre-Segura, 2013). The least known European species is Sciobia (Thliptoblemus) barbara Saussure, 1877, now Sciobia (Thliptoblemus) natalia Gorochov, 1985. It is common in Morocco (see review in Chopard, 1943), however, we know virtually nothing about its biology and current European distribution. In fact, the only report to date for Europe (SW Spain) comes from the naturalist M.M. Escalera (1867-1949). He collected one male and one female from Algeciras (Cádiz, province) and donated the specimens to the Museum of Entomology of Madrid (now Museo Nacional de Ciencias Naturales, MNCN). Up to now, all bibliographic literature mentioning the species in Europe (Spain) have Escalera's specimens from Algeciras as the only reference, either as S. (T.) barbara (Bolívar, 1925; Bolívar, 1927; Harz, 1969) or as S. (T.) natalia (Gorochov & Llorente, 2001; Barranco & Aguirre-Segura, 2013). Although, specimen labels have no date of capture, we can estimate roughly the date of Escalera donation occurring between 1914 and 1925. Bolívar (1914) (216p.) did not mention S. (T.) barbara for Spain in his “Dermaptera and Orthopterans of Morocco” which he did for other Moroccan species also present in Spain. However, he mentioned it in his paper on “Contribution to the knowledge of Sciobiae” (Bolívar, 1925) (431p.).

In this paper, we report the presence of S. (T.) natalia for Cádiz province and bring information useful for a better understanding of the distribution and biology of the European meta-population of this intriguing species. These data are crucial for its better conservation. To attain this, we performed several field campaigns in Cádiz and surrounding provinces in search of the species and collected information on its distribution, adding notes on its habitats, phenology and behaviour. We also include comparative analyses of the songs of S. (T.) natalia and its co-distributed species, S. (T.) caliendrum.

During the course of our research projects on fragmentation of small populations of orthopterans, we followed methods used in previous works emphasizing on field collecting data to track rare species of crickets (Cordero et al., 2007; Cordero & Llorente, 2008). We prospected potential areas in Cádiz and surrounding provinces during different seasons and years, searching for crickets on the ground, under stones, or by detecting their specific song in the field. Field campaigns took place several days in July 2006, August and October 2012; May and June 2014, and May 2015. We only found the species on May and June. Whe hearing Sciobiae species, we used car transects in rural pathways and secondary roads to detect singing plots along hedgerows and edges of open fields on May (2014, 2015) and June (2014). Once detected a Sciobia (T.) singing plot, we examined the area in search of the species, whenever conditions were feasible, to increase the prospected territory. We did not attempt to obtain the full current distribution of Sciobia (T.) natalia, but to reveal its current presence in the study area at as many plots as possible. We analysed male songs of Sciobia (T.) natalia and Sciobia (T.) caliendrum in the lab. Recording was under identical conditions for both species, at 21 °C temperature and in the same hour and day in order to compare oscilograms and sonograms. We used a digital audio recorder Tascam HD-P2, with a K6-M66 Sennheiser microphone and followed the methods described elsewhere (Cordero et al., 2009). We also captured some females to obtain data on breeding under lab conditions. We maintained one female alive in 2014 and 2 in 2015, at room temperature and natural light regime with limited sun exposure to prevent excess of temperature. We kept individuals in plastic boxes for domestic pets with a 2-3 cm depth of soil mix containing 75% of commercial peat for flowering plants and 25% of sand, or just with soil directly from the area of capture (Almodovar reservoir). We maintained individuals alive in the lab, recording dates of hatching of nymphs and adult deaths.

CAPTURE POINTS, GPS DATA, DATES AND SPECIMENS

Specimens collected are similar to those of Escalera (Algeciras) (Fig. 1a, b) although the largest out of four males presents the facial protuberance that Gorochov & Llorente (2001) mentioned for S. (T.) natalia from Morocco. The study of the taxonomic status of this population will be published somewhere else. We list below plots with detected presence of S. (T.) natalia Data points are represented in Fig. 2

36°9′32.07′′N, 5°38′20.87′′O (UTM: 30S 262594, 4004801). May-31^st-2014; May-25^th-2015. Almodovar's Reservoir, Facinas, Tarifa (Cádiz province, Spain). 2♂♂, 2♀♀ and 1♀ respectively.

HABITAT, ECOLOGY AND BEHAVIOUR OBSERVATIONS

The species is local and occasionally abundant in open pasture meadows and road or pathways hedgerows during the maximum vegetative growth of herbaceous plants in May and June (Fig. 3). Adults are very active during the day, singing in choruses and moving around in a similar way that the codistributed S. (T.) caliendrum (Fischer, 1853) does, probably coinciding with courtship period. Sciobia (T.) natalia inhabits clay and loamy soils that crack when dried, allowing abundant underground refuges, although they also occupy temporary refuges under stones. They occur in non-cultivated fields and meadows, particularly in the proximities of water reservoirs, in open land of cattle states with several grasses and other herbaceous plants like Daucus, Cynara, Malva or the predominant Scolymus hispanicus scattered with small patches of bare ground i.e., typical cattle grazing land. We found it at the edges of the fields, and open hedgerows probably because of minor influence of cattle and more dense herbaceous vegetation. In three of the four localities mentioned (points 1, 2, and 4), S. (T.) natalia coexisted with the more abundant, widespread and conspicuous S. (T.) caliendrum, a species that presents a relatively wider distribution and ecological spectrum, occupying more diverse and drier plots, including those with scarce vegetation in mountainous areas of Sierra de Grazalema (data for this species not shown). The highest concentration of S. (T.) natalia occurred in point 3, on May 31^st, 2014. Density was around 0.25 individuals per square meter in a humid hedgerow plot (225×15 m) of bare ground and dense tall grasses (Avena, Brachypodium, Polypogon) influenced by the “Pozo del Gallego” stream that crosses it in the lower side of the plot. This is the only plot in which S. (T.) caliendrum did not co-occur with S. (T.) natalia. On June 14^th 2014, vegetation at this point was drier and we did not detect any individual by direct recording. On May 26^th 2015, horses grazed out, trampled the grass and eutrophicated the ground in this point; humidity was also lower than in previous year. We could not record any individual neither.

In Almodovar and Barbate reservoirs (points 1 and 2), both species coexisted although S. (T.) natalia seemed to be more frequent than S. (T.) caliendrum in Almodovar (a plot of dense herbaceous vegetation, on May 2014). In Barbate's shores, we only found S. (T.) natalia in small plots of dense open herbaceous vegetation whereas S. (T.) caliendrum was extraordinary abundant (song choruses and direct observations) in neighbour large plots with sparse scrubs, trees and stony ground with more proportion of bare ground. For both reservoirs, May 2014 was better than May 2015 and June 2014 was negative for direct observations of S. (T.) natalia, but nor for S. (T.) caliendrum.

In point 4, S. (T.) caliendrum was predominant all around both in May 2014 and 2015, but we identified only one specimen of S. (T.) natalia on June 14^th 2014. We recorded one male close to the edge of a state with abandoned and sparse olive trees with some scrubs and high herbaceous vegetation, mainly Scolymus hispanicus. The presence of sparse trees, high scrubs and herbaceous vegetation together with certain humidity due to the proximity of Ballesteros stream probably facilitated the presence of S. (T.) natalia.

Hatching in the lab occurred on some date of first half of July 2014 and on July 2^nd and July 9^th for the 2015 females. Adults died between mid-June and the end of July whereas nymphs overwintered, those of 2014 becoming adults on May 2015. Nymphs of S. (T.) natalia present the darkest colouration compared with the rest of other Iberian Sciobia nymphs species, changing to black jet, particularly on head and pronotum from November-December onwards (Fig. 4). The species presents a univoltine reproductive cycle. Nymphs could spend between 8-9 months in subterranean galleries and crevices, so that the type and structure of the soil may be of great importance for the species. We could not find any nymph under stones in any other prospecting campaigns of July 2006, August 2012 or October 2012. Nymphs eventually could come up to surface by night or in periods of heavy rain as it may occur in other cricket species.

To the human ear, the song uttered by S. (T.) natalia can be distinguished from that of S. (T.) caliendrum. It is shorter, raspy, less intense and less musical than in S. (T.) caliendrum. In Fig. 5, we depict waveforms and spectrograms. Sciobia (T.) caliendrum shows a more continuous singing activity than S. (T.) natalia. Chirps are quite different between species. Chirps are 100ms in length with an uniform, low amplitude decay of 100-200 ms long (Fig. 5C) and are composed of 6-9 syllables of regular amplitude with the first to third increasing progressively and maintaining this maximum to the end (Fig. 3E). The syllable presents amplitude modulation (Fig. 5G) at 6 and 5 KHz respectively (Fig. 5I) related with a trill-type sound effect. On the contrary, S. (T.) natalia chirp is longer (250-350 ms) (Fig. 5D) with an average of 25 syllables per chirp (range 23-28) and a progressive amplitude with sharp end (Fig. 5F). The syllable presents an only component at 7 Khz (Fig. 5H).

Our observations suggest that S. (T.) natalia is not as rare as expected within the open landscape of part of Cádiz province. According to our observations, it prefers more dense vegetation as we did not find it in either drier or bare grounds where S. (T.) caliendrum may still be present. However, more intense study is necessary to attain a full picture of habitat variation for S. (T.) natalia and its full distribution in SW Spain.

WHY WE HAVE NO RECORDS OF S. (T.) NATALIA SINCE ESCALERA FOUND IT FROM ALGECIRAS?

Several factors may have contributed to this situation: (1) Factors related with the species specific behaviour and distribution. The distribution range of the species in the Iberian Peninsula, although still probably incomplete, is most likely very small. Further, its behaviour is cryptic, preferring dense herbaceous vegetation where individuals are more difficult to find. The species is probably active and visible only a few weeks in a year, spending most of the time in underground galleries and deep soil crevices, particularly in nymphal stages. According to our observations, it is probable that yearly climate fluctuations change population sizes or modify conspicuous behaviour, and thus the numbers of individuals detected in the field may change enormously year-to-year. (2) According to our field observations, we believe that an important reason for S. (T.) natalia going unnoticed is the coexistence in mosaic areas of appropriate microhabitats with S. (T.) caliendrum, a more conspicuous relative species. In the appropriate dates, S. (T.) caliendrum is extraordinary noisy and visible in areas where S. (T.) natalia can also be present. Sciobia (T.) caliendrum may be present at high densities in certain plots where choruses are heard everywhere with a louder and ubiquitous song, masking the presence of S. (T.) natalia, even if recognized by ear. Under the same situation, most of the visual contacts are for S. (T.) caliendrum that is easier to find in plots with bare ground or with short or sparse vegetation. A shallow evaluation probably result in S. natalia going unnoticed, which may be the case in some of the many areas in which we found S. (T.) caliendrum. (3) The lack of researchers devoted to studies of classical taxonomy, species discovery, descriptive work on faunistics of arthropods and prone to combine museum with field research. This is a serious problem for biodiversity assessment and respond to the low promotion value and poor funding of these kind of studies, particularly neglected for many decades (e.g. Wheeler et al., 2004).

CONSERVATION CONCERNS

The crowd courtship of Sciobia (T) crickets, singing and moving in large numbers in certain plots of the Cádiz province, is an entomological phenomenon worth preserving for Europe. The limited extension of the distribution area of S. (T.) natalia and its dependence on anthropic habitats submitted to changes in land use may enhance hazardous threats for populations in small geographic areas. Unexpected changes in agricultural policy like over-increasing cattle density (as in other Spanish Regions); changes of land use for agriculture, a widespread misuse of pesticides or the introduction of harmful alien species for Sciobiae, are human-dependent factors that should be avoided. Stochastic factors like long and severe droughts or important flooding events may also influence populations negatively in a region particularly vulnerable to climate oscillations (e.g. Giorgi & Lionello, 2008). Conservation measures should include the knowledge of the existence of the species, the recognition of its habitats and the maintenance of traditional land uses.