Polymorphism and Divergence of Multilocus DNA Markers in Sibling Species Chironomus riparius Meigen and Chironomus piger Strenzke (Diptera,Chironomidae)

Intra- and interspecific variation and divergence of multilocus markers for genomic DNA of the sibling species from the thimmi group,Chironomus riparius and C. piger, were studied by PCR with arbitrary primers (RAPD). A high level of RAPD polymorphism was determined in both laboratory and natural populations of these species. The genetic distances were estimated between the C. riparius populations and between the sibling species C. riparius and C. piger. The genetic distance between C. riparius andC. piger was 4 to 5 times higher than that between the C. riparius populations. A comparison of the variation and divergence for the RAPD markers with those for other genomic markers—enzyme-coding genes and chromosomes (gene linkage groups)—showed that different components of the genome differed in their contribution to the genome divergence.     

Evolutionary determinants of population differences in population growth rate × habitat temperature interactions in Chironomus riparius

Little is known about intraspecific variation in fitness performance in response to thermal stress among natural populations and how this relates to evolutionary aspects of species ecology. In this study, population growth rate (PGR; a composite fitness measure) varied among five natural Chironomus riparius populations sampled across a climatic gradient when subjected to three temperature treatments reflecting the typical range of summer habitat temperatures (20, 24 and 28 °C). The variation could be explained by a complex model including effects of genetic drift, genetic diversity and adaptation to average temperature during the warmest month, in addition to experimental temperature. All populations suffered a decrease in PGR from 20 to 28 °C and ΔPGR was significantly correlated with the respective average habitat temperature in the warmest month—populations from warmer areas showing lower ΔPGR. This implies that long-term exposure to higher temperatures in the warmest month (the key reproductive period for C. riparius) is likely to be a key selective force influencing fitness at higher temperatures. A comparison of phenotypic divergence and neutral genetic differentiation revealed that one phenotypic trait—the number of fertile egg masses per female—appeared to be under positive selection in some populations. Our findings support a role for response to temperature selection along a climatic gradient and suggest population history is a key determinant of intraspecific fitness variation. We stress the importance of integrating different types of data (climatic, experimental, genetic) in order to understand the effects of global climate change on biodiversity.     

Complex relations between freshwater macro- and meiobenthos: interactions between Chironomus riparius and Chydorus piger

• 1 The potential importance of interactions between macro- and meiobenthos in the littoral zone of takes was studied in a series of laboratory experiments with a chironomid and a chydorid.
• 2 In a situation of intraspecific density dependence, Chydorus piger Sars inhibited the growth of Chironomus riparius Meigen, while both second- and fourth-instar C, riparius stimulated the parthenogenetic reproduction of C. piger.
• 3 The meiofaunal chydorids may thus have a structuring effect on macrofaunal chironomid populations by interfering with the early-instar larvae.
• 4 With macro- and meiofaunal species both operating at the primary consumer-level of the food web, this kind of complex interaction will affect the magnitude of secondary production available to higher trophic levels.

     

Development and localization of microsatellite markers for the sibling species Chironomus riparius and Chironomus piger (Diptera: Chironomidae)

Five variable microsatellite loci are reported for the nonbiting midge species Chironomus riparius and Chironomus piger. All loci show considerable intraspecific variation and species‐specific alleles, which allow to discriminate among the two closely related species and their interspecific hybrids, and to estimate genetic diversity within and between populations. Additionally, the loci were localized on C. riparius polytene chromosomes to verify their single copy status and investigate possible chromosomal linkage. The described markers are used in different studies with regard to population and ecological genetics and evolutionary ecotoxicology of Chironomus.     

Thermal influences on the habitat preference and the diurnal activity in three European Rana species

The diurnal behaviour of frogs was recorded quantitatively in a habitatlike experimental environment by a new method of automatic registration via thermocouples. Three species with different habitat preferences during their summer activity period were chosen: the terrestrial common frog Rana temporaria LINNÈ and the semiaquatic water frog Rana lessonae CAMERANO and Rana ridibunda PALLAS. The activity, the location and the skin temperatures of these frogs were recorded continuously in four different temperature ranges (8.1° C–31.0° C) within the temperature span of the summer activity period. The thermal requirements and behavioural adaptations to the habitat of each species were analysed. The experimental results coincided with field observations and showed some details not yet known. The northern species R. temporaria exhibited a distinctive behavioural thermoregulation including cooling behaviour at high temperatures and warming behaviour at low temperatures during the day. In all temperatures tested these frogs remained on land changing their preferred location from the open area to the hiding places. The main activity period shifted from night to day with decreasing temperatures. The more southern species R. lessonae preferred higher temperatures than the other species showing basking behaviour during the day independent of the ambient temperature. With decreasing temperatures the preferred location changed from the shore to the water and the activity during the night almost disappeared. The closely related R. ridibunda tolerated high temperatures too, but only rarely basked. This species, however, reacted contrarily to decreasing temperatures: it changed its preference from the water to the land. This behavioural differenciation between the water frog species may be of importance for the actual habitat preference of these central european water frogs.     

Mechanisms of species coexistence: a field test of theoretical models using intertidal snails

Competitor coexistence is often facilitated by spatial segregation. Traditionally, spatial segregation is predicted to occur when species differ in the habitat in which they are either superior at competing for resources or less susceptible to predation. However, predictions from a behavioural model demonstrate that spatial segregation and coexistence can also occur in the absence of such interspecific trade‐offs in competitive ability and vulnerability to predation. Unlike other models of competitor coexistence this model predicts that when species rank both habitat productivity and ‘riskinesses’ similarly, but differ slightly in their habitat‐specific vulnerabilities to predators, they will tend to segregate across habitats, with the species experiencing the higher ratio of mortality risk across the habitats occurring primarily in the safer habitat. Here, we investigate the hypothesis that intraspecific trade‐offs between resource availability and mortality risk can lead to spatial segregation of competing species by (1) documenting the spatial (i.e. intertidal) distribution of two marine snails, Littorina sitkana and L. subrotundata and (2) performing field experiments to quantify growth and mortality rates of each species at ‘low’ and ‘high’ intertidal heights. Our results indicate that both species agree on the rankings of habitat riskiness and productivity, experiencing higher predation and higher growth in low‐ than in high‐intertidal habitats. However, L. sitkana and L. subrotundata experienced differences in their habitat‐specific mortality risks and growth rates. Despite both species being similarly at risk of predation in high‐intertidal habitats (where mortality was lower), L. subrotundata was subject to significantly higher mortality than L. sitkana at the low‐intertidal height. In contrast, growth rate differences between habitats were greater for L. sitkana than for L. subrotundata. Whereas both species grew at the same rate at the high‐intertidal level (where growth was lower), L. sitkana individuals grew more rapidly than L. subrotundata snails at the low‐intertidal level. As predicted by the behavioural model, the species that experienced the higher ratio of mortality across habitats (i.e. L. subrotundata) occurred exclusively in the safer, high‐intertidal habitat. Taken together, these results provide support for the hypothesis that spatial segregation, and potentially competitor coexistence, can occur in the absence of interspecific trade‐offs in resource acquisition ability or vulnerability to predation.     

Reproductive isolation and ecological niche partition among larvae of the morphologically cryptic sister species Chironomus riparius and C. piger

Background

One of the central issues in ecology is the question what allows sympatric occurrence of closely related species in the same general area? The non-biting midges Chironomus riparius and C. piger, interbreeding in the laboratory, have been shown to coexist frequently despite of their close relatedness, similar ecology and high morphological similarity.

Methodology/Principal Findings

In order to investigate factors shaping niche partitioning of these cryptic sister species, we explored the actual degree of reproductive isolation in the field. Congruent results from nuclear microsatellite and mitochondrial haplotype analyses indicated complete absence of interspecific gene-flow. Autocorrelation analysis showed a non-random spatial distribution of the two species. Though not dispersal limited at the scale of the study area, the sister species occurred less often than expected at the same site, indicating past or present competition. Correlation and multiple regression analyses suggested the repartition of the available habitat along water chemistry gradients (nitrite, conductivity, CaCO₃), ultimately governed by differences in summer precipitation regime.

Conclusions

We show that these morphologically cryptic sister species partition their niches due to a certain degree of ecological distinctness and total reproductive isolation in the field. The coexistence of these species provides a suitable model system for the investigation of factors shaping the distribution of closely related, cryptic species.     

Structural differentiation of microhabitats of sympatricmacaca fascicularis andM. nemestrina in East Kalimantan,Indonesia

Macaca nemestrina andM. fascicularis coexist through much of their geographic ranges in Southeast Asia, but locally they segregate into drier hilly terrain and wetter alluvial riverine terrain respectively. SinceM. fascicularis travel arboraally andM. nemestrina, travel terrestrially, structural characteristics of habitats on the two different substrates may explain local segregation of these two species. This paper reports measures comparing habitat structure ofM. fascicularis fascicularis andM. nemestrina nemestrina at the Mentoko site in East Kalimantan, Indonesia. Results show that (1) ground cover is thicker; (2) there are fewer gaps in the canopy; and (3) the foliage of the canopy is more dense in habitat occupied by arborealM. f. fascicularis than in habitat occupied byM. n. nemestrina. These differences in habitat structure appear to explain segregation of the two species at the Mentoko. Similar differences in habitat may permit coexistence of the two species throughout their geographical ranges.     

Density‐dependent habitat selection predicts fitness and abundance in a small lizard

Density‐dependent habitat selection has been used to predict and explain patterns of abundance of species between habitats. Thermal quality, a density‐independent component of habitat suitability, is often the most important factor for habitat selection in ectotherms which comprise the vast majority of animal species. Ectotherms may reach high densities such that individual fitness is reduced in a habitat due to increased competition for finite resources. Therefore, density and thermal quality may present conflicting information about which habitat will provide the highest fitness reward and ectotherm habitat selection may be density‐independent. Using ornate tree lizards Urosaurus ornatus at 10 sites each straddling two adjacent habitats (wash and upland), we tested the hypothesis that habitat selection is density‐dependent even when thermal quality differs between habitats. We first tested that fitness proxies decline with density in each habitat, indicating density‐dependent effects on habitat suitability. We also confirmed that the two habitats vary in suitability (quantified by food abundance and thermal quality). Next, we tested the predictions that habitat selection depends on density with isodar analyses and that fitness proxies are equal in the two habitats within a site. We found that monthly survival rates decreased with density, and that the wash habitat had more prey and higher thermal quality than the upland habitat. Lizards preferred the habitat with more food and higher thermal quality, lizard densities in the two habitats were positively correlated, and fitness proxies of lizards did not differ between habitats. These patterns are consistent with density‐dependent habitat selection, despite differences in thermal quality between habitats. We expect that density‐dependent habitat selection is widespread in terrestrial ectotherms when densities are high and temperatures are close to their optimal performance range. In areas where thermal quality is low, however, we expect that depletable resources, such as food, become less limiting because assimilating resources is more difficult.     

The influence of potential stressors on oviposition site selection and subsequent growth,survival and emergence of the non‐biting midge (Chironomus tepperi)

Theory predicts that animals should prefer habitats where their fitness is maximized but some mistakenly select habitats where their fitness is compromised, that is, ecological traps. Understanding why this happens requires knowledge of the habitat selection cues animals use, the habitats they prefer and why, and the fitness costs of habitat selection decisions. We conducted experiments with a freshwater insect, the non‐biting midge Chironomus tepperi to ask: (a) whether females respond to potential oviposition cues, (b) to explore whether oviposition is adaptive in relation to metal pollution and conductivity, and (c) whether individuals raised in poor quality sites are more likely to breed in similarly poor locations. We found the following: (a) females responded to some cues, especially conductivity and conspecifics, (b) females preferred sites with higher concentrations of bioavailable metals but suffered no consequences to egg/larval survival, (c) females showed some avoidance of high conductivities, but they still laid eggs resulting in reduced egg hatching, larval survival, and adult emergence, and (d) preferences were independent of natal environment. Our results show that C. tepperi is susceptible to ecological traps, depending on life stage and the relative differences in conductivities among potential oviposition sites. Our results highlight that (a) the fitness outcomes of habitat selection need to be assessed across the life cycle and (b) the relative differences in preference/suitability of habitats need to be considered in ecological trap research. This information can help determine why habitat preferences and their fitness consequences differ among species, which is critical for determining which species are susceptible to ecological traps.     

Assessing the sensitivity of Melanoplus frigidus (Orthoptera: Acrididae) to different weather conditions: A modeling approach focussing on development times

The temperature and soil moisture conditions as well as vegetation patterns were studied to describe the habitat and to model the life cycle of Melanoplus frigidus, a true alpine grasshopper of the Scandes. In the low alpine belt of the Norwegian Scandes the species colonizes only the warmest microhabitats with maximum soil surface temperatures of 31°C. Vegetation of these habitats consists of shrub‐rich heath dominated by Vaccinium myrtillus and Calluna vulgaris. Using continuously measured temperature data, the development times for four different seasons were modeled and related to field observations. The maximum delay of adult molt was estimated to amount to 3 weeks, the delay being determined by the variation in spring temperature conditions between different years. The possibilities of using M. frigidus as an indicator organism of climate change effects on alpine zoo‐coenoses of the Scandes are discussed.     

Habitat segregation in four species of adult tiger beetles (Coleoptera: Cicindelidae)

ABSTRACT.

• 1 Habitat segregation in four species of tiger beetles, Cicindela cancellata Dejean, C.cardoni Fleutians, C.minuta Olivier and C.sumatrensis Herbst in a river bank ecosystem was studied in dry and wet seasons.
• 2 The four species segregated distinctly along the river beds into separate habitats, with occasional overlapping in both the seasons.
• 3 Among the habitat characteristics considered, vegetation, soil moisture and available prey-size were found to be important in species segregation.
• 4 D ²-analysis showed that the habitat preferences of C.cardoni and C.cancellata were closer to that of C.sumatrensis. The habitat of C.minuta was distinctly separated.
• 5 There was a positive correlation between the mandible length of each tiger beetle species and the length of prey captured.
• 6 Variance in mandible length within species was related to prey-length distribution pattern and to variance in habitats.

     

Invasion of north European streams by brook trout: hostile takeover or pre-adapted habitat niche segregation?

We combine evidence from small-scale experiments with a large-scale field survey to clarify the roles of biotic resistance and pre-adapted habitat niche segregation to the invasion success of the North American brook trout (Salvelinus fontinalis) in North European streams previously dominated by brown trout (Salmo trutta). Interspecific aggressions among the two species were negligible, yet there was distinct habitat niche segregation between them: brook trout occupied mainly pool habitats while brown trout tended to reside in fast-flowing riffles. Habitat niche segregation among brook trout and brown trout prevailed across a wide array of scales from experimental flumes to entire drainage systems, although the segregation pattern was weaker in the field. Habitat differentiation among the two species reflected their differential habitat requirements, suggesting that a match between a species’ niche requirements in its native range and habitat availability in the new environment is a prerequisite for understanding invasion success.     

Potential effects of spawning habitat changes on the segregation of northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) and muskellunge (<Emphasis Type="Italic">E</Emphasis>. <Emphasis Type="Italic">masquinongy</Emphasis>) in the Upper St. Lawrence River

Changes in spawning habitat of northern pike (Esox lucius) may affect their segregation from and coexistence with the closely related muskellunge (E. masquinongy). We estimated the areal coverage of robust and shallow emergent vegetation in three shared-spawning bays in the Upper St. Lawrence River from aerial photographs taken from 1948 to 2003. Robust emergent vegetation (e.g., cattail) increased in coverage by 155–241% while shallow emergents (sedges) decreased by 46–96%. The loss of sedges, an important northern pike-spawning habitat, may facilitate greater spawning overlap in offshore-submersed aquatic vegetation within bay habitats used by muskellunge. Development rates and characteristics of northern pike and muskellunge eggs and larvae were compared to better understand the implications of greater spawning overlap. Northern pike eggs developed faster than muskellunge eggs at temperatures of 4.7–19°C, and adhesive eggs and the presence of adhesive papillae were present in both species. Equations were used to predict degree-day requirements for hatching and swim-up in three habitats (shallow emergents, bay, and offshore shoal) along a temperature gradient. Northern pike required more estimated degree days to reach hatching in bay and offshore shoal habitat relative to shallow emergent habitat due to cooler temperatures. Significant spawning overlap is known to occur within bay habitats, but poor success of northern pike in deep bay habitats and overall reductions in abundance are hypothesized to currently buffer muskellunge from potential negative interactions between these species. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

GERMINATION ECOLOGY OF DANTHONIA SERICEA POPULATIONS

Seed were collected from nine populations of Danthonia sericea on either wet or well-drained, sandy sites ranging from Georgia to New Jersey. Germination tests were conducted in the laboratory and in field plots established on contrasting habitat types. Factors considered were temperature, light, prechilling, scarification, and after-ripening. The majority of freshly harvested seed from all nine populations exhibited innate dormancy the intensity of which decreased with age. Dormancy was removed by scarification and prechilling treatments of 60 days. Seed from wet habitats showed significantly greater germination in light (alternating night-day) than in dark, while seed from well-drained habitats had a higher germination percentage in dark than in light. Both responses are considered to be physiological adaptations of the populations to their respective habitats. Alternating night-day temperatures of 15–25 C produced the greatest overall germination for the nine populations; 15–20 and 10–25 C produced the next highest responses. Field observations confirmed that peak germination occurred in the spring, at the time soil temperatures were in the same range found to be optimum in the laboratory. A comparison of the germination responses obtained from six New Jersey populations in field plots on contrasting habitat types further revealed distinctive physiological adaptations for populations from differing habitats.     

Thermal niche variation among individuals of the poison frog,Oophaga pumilio,in forest and converted habitats

The conversion of natural habitats to human land uses often increases local temperatures, creating novel thermal environments for species. The variable responses of ectotherms to habitat conversion, where some species decline while others persist, can partly be explained by variation among species in their thermal niches. However, few studies have examined thermal niche variation within species and across forest‐land use ecotones, information that could provide clues about the capacity of species to adapt to changing temperatures. Here, we quantify individual‐level variation in thermal traits of the tropical poison frog, Oophaga pumilio, in thermally contrasting habitats. Specifically, we examined local environmental temperatures, field body temperatures (T_b), preferred body temperatures (T_pref), critical thermal maxima (CT_max), and thermal safety margins (TSM) of individuals from warm, converted habitats and cool forests. We found that frogs from converted habitats exhibited greater mean T_b and T_pref than those from forests. In contrast, CT_max and TSM did not differ significantly between habitats. However, CT_max did increase moderately with increasing T_b, suggesting that changes in CT_max may be driven by microscale temperature exposure within habitats rather than by mean habitat conditions. Although O. pumilio exhibited moderate divergence in T_pref, CT_max appears to be less labile between habitats, possibly due to the ability of frogs in converted habitats to maintain their T_b below air temperatures that reach or exceed CT_max. Selective pressures on thermal tolerances may increase, however, with the loss of buffering microhabitats and increased frequency of extreme temperatures expected under future habitat degradation and climate warming. Abstract in Spanish is available with online material.     

Temperature requirements for the growth of young sporophytes of Undaria pinnatifida and Undaria undarioides (Laminariales, Phaeophyceae)

The relative growth rate of young sporophytes of Undaria pinnatifida (Harvey) Suringar and Undaria undarioides (Yendo) Okamura was examined in order to understand the difference in distribution of these two species around the coast of Japan. The optimal temperature for growth of both species was similar at 20°C and the upper critical temperature for growth was also similar, at 27°C for U. pinnatifida and 26°C for U. undarioides. Therefore, the optimal and upper critical temperatures for growth of the young sporophytes are not the main factors determining the distribution of each species. Next, the lower critical temperatures for growth were examined. For the young sporophytes of U. pinnatifida, the lower limit was less than 5°C while for those of U. undarioides it was 15°C. Thus, the difference in the lower critical temperature for growth between the two species was approximately 10°C. During the period of young sporophyte growth in the field, the temperature at the mouth of Ise Bay, Japan, where U. pinnatifida occurs, ranges from 12.7°C in December to 13.1°C in April, with a minimum of 7.9°C in February. Our experiments indicate that young sporophytes are able to grow throughout this period. The temperature off Hamajima, Japan, where U. undarioides occurs, ranges from 19.1°C to 14.8°C during the same time period. Again, young sporophytes are able to growth throughout this period, although minimum winter temperatures are only just high enough for growth. These natural temperature ranges during the growth season of the sporophytes agree well with the experimentally determined temperature requirements for growth of each species. Therefore, the difference between the two species in the critical temperature required for growth of the young sporophytes, especially in the low temperature range, is one of the major factors determining the distribution pattern of each species.     

Differential Habitat Selection by Pygmy Grasshopper Color Morphs; Interactive Effects of Temperature and Predator Avoidance

Habitat selection behavior is affected by complex interplays between competing requirements. Here we combine field observations with laboratory experiments to examine how thermal benefits and predator avoidance influences habitat selection by different color morphs of the pygmy grasshopper Tetrix undulata. The composition of substrate types and surface temperatures in areas selected by free-ranging individuals did not reflect relative availability, and varied among morphs and sexes. Surface temperatures of selected habitats deviated less from the range of preferred body temperatures than would result from a random utilization of surface temperatures, suggesting that grasshoppers selected habitats with thermal properties which were suitable for maintaining preferred body temperatures. The thermal property of habitats occupied by different color morphs suggests that darker morphs (which absorb more solar radiation) selected cooler habitats to avoid overheating. Dissimilarities in substrate use among color morphs in the field and laboratory emphasize a role also of predator avoidance by background matching for habitat choice. The degree of habitat selectivity was lowest in the striped morph, supporting the notion that a disruptive color pattern may constitute a solution to the trade-off between relative crypsis in different visual backgrounds. Finally, individuals modified their habitat use when subjected to elevated risk of predation, showing that habitat choice is governed by conflicting priorities. Collectively, our findings suggest that, as a result of direct and indirect effects of coloration on performance, alternative color morphs use different solutions to the trade-off between competing requirements. Our results also lend support to the notion that relative fitness of alternative color morphs and sexes may be dependent on microhabitat selection, as predicted by the theory of multiple niche polymorphisms.     

The evolution of redd site selection in brook charr in different environments: same cue,same benefit for fitness*

1. Despite the great interest in characterising fish reproductive habitat, the relationship between the selection of a given spawning site and individual fitness has not been experimentally tested. 2. In this study, we used an in situ experimental approach to determine (i) the relative contribution of substrate characteristics as well as hydrological and physicochemical variables to small‐scale redd site selection by brook charr, Salvelinus fontinalis (Mitchill) and (ii) if hatching and emergence success, used as a surrogate of fitness, are improved in selected compared to non‐selected sites in both lake and stream habitats. 3. Our results show that upwelling groundwater flow was always significantly higher in selected than in non‐selected sites in both lake and stream habitats. We found no significant difference in the mean geometric substrate diameter and no consistent differences in substrate composition between selected and non‐selected sites. Oxygen concentration was higher (significantly so in three of four comparisons) and conductivity tended to be lower in selected than in non‐selected sites, while temperature showed no significant or consistent variations. We found a significant positive relationship between the selection of a given spawning habitat and hatching and emergence success in these systems. 4. These results show that the main cue that brook charr use to select their spawning sites is upwelling groundwater in lake and stream habitats, and that active selection of these sites increases individual fitness. This suggests that natural selection acted on the same cues in lentic and lotic environments; this could have been highly adaptive in a species that used both habitats as colonisation routes after the last glaciation.     

Somatic breakpoints,distribution of repetitive DNA and non-LTR retrotransposon insertion sites in the chromosomes of <Emphasis Type="Italic">Chironomus piger</Emphasis> Strenzke (Diptera,Chironomidae)

Structural aberrations, their frequency and distribution as well as distribution of the tandem repetitive minisatellite DNA clusters of Alu and Hinf elements and two retroelements, the LINE NLRCth1 and the SINE CTRT1, were analyzed in the genome of the chironomid C. piger Strenzke larvae from a Bulgarian population. A consistent somatic variability in the structure of the polytene chromosomes was detected, showing that the C. piger genome is more actively rearranging than supposed before. Breakpoints were concentrated in proximal parts of chromosomes significantly more often than in distal parts. By FISH analysis we could detect only one locus containing Alu elements and 38 Hinf cluster loci which appear to be dispersed equally all over the chromosomes. The retrotransposons NLRCth1 and CTRT1 are present only in a few loci, but highly variant among different individuals. The mean number of NLRCth1 sites per individual was 18.4 ± 2.09 and of CTRT1 was 54.8 ± 8.42. A third of breakpoint locations were close to or coincide with a locus occupied by a retroelement (either NLRCth1 or CTRT1). Nineteen percent of breakpoints coincided with Hinf repetitive DNA elements. Some breakpoints were identical in the two sibling species C. piger and C. riparius Meigen (syn.: C. thummi thummi) and are considered as conserved hot spots of chromosome breakage.