Appendage abnormalities in spiders induced by an alternating temperature protocol in the context of recent advances in molecular spider embryology.

In the literature there are numerous reports of developmental deformities in arthropods collected in their natural habitat. Since such teratogenically affected individuals are found purely by chance, the causes of their defects are unknown. Numerous potential physical, mechanical, chemical, and biological teratogens have been considered and tested in the laboratory. Thermal shocks, frequently used in teratological research on the spider Eratigena atrica, have led to deformities on both the prosoma and the opisthosoma. In the 2020/2021 breeding season, by applying alternating temperatures (14 °C and 32 °C, changed every 12 h) for the first 10 days of embryonic development, we obtained 212 postembryos (out of 3,007) with the following anomalies: oligomely, heterosymely, bicephaly, schistomely, symely, polymely, complex anomalies, and others. From these we selected six spiders with defects on the prosoma and two with short appendages on the pedicel for further consideration. The latter cases seem particularly interesting because appendages do not normally develop on this body part, viewed as the first segment of the opisthosoma, and appear to represent examples of atavism. In view of the ongoing development of molecular techniques and recent research on developmental mechanisms in spiders, we believe the observed phenotypes may result, at least in part, from the erroneous suppression or expression of segmentation or appendage patterning genes. We consider "knockdown" experiments described in the literature as a means for generating hypotheses about the sources of temperature-induced body abnormalities in E. atrica.

Teratological changes in postembryos of Eratigena atrica obtained by the application of alternating temperatures on spider embryos.

Spider embryonic development depends on several factors, including temperature. Under optimum thermal conditions embryogenesis proceeds undisturbed and embryo mortality is low. On the other hand, dramatic shifts in incubation temperature may cause a range of developmental defects in embryos. It has been confirmed in numerous laboratory experiments that abrupt temperature changes can be a powerful teratogenic factor. Changes in the external structure are frequently reflected in the internal anatomy, and above all, in the central nervous system. In the present teratological study, by exposing spider embryos to the temperatures of 14 °C and 32 °C, changed every 12 hours for the first 10 days of their development, we obtained 74 postembryos of Eratigena atrica with body deformities such as oligomely, heterosymely, schistomely, bicephaly, complex anomalies and others. We selected six spiders to describe and analyze their morphological changes. In one case, that of a spider affected by polymely (the presence of a supernumerary appendage) combined with heterosymely (the fusion of walking legs), we also focused on the structure of the central nervous system. The analysis indicated that this complex anomaly was accompanied by only one change in the central nervous system: the presence of a supernumerary neuropil. Since no fusion of walking leg neuropils was observed, it was concluded that, in this instance, there was no relationship between the fusion of legs and the structure of the central nervous system.

The effect of temperature and light on embryogenesis and post-embryogenesis of the spider Eratigena atrica (Araneae, Agelenidae).

Embryogenesis and post-embryogenesis of spiders depend on several environmental factors including light and temperature. This study was aimed at evaluating the impact of different thermal and lighting conditions on embryonic and early post-embryonic development of Eratigena atrica. Embryos, larvae, nymphs I and II were incubated at constant temperatures of 12, 22, 25 and 32°C under three different light regimes: light, dark, light/dark. Extreme temperatures (12 and 32°C) significantly increased mortality of embryos (to 100%) and nymphs II, whereas larvae and nymphs I suffered reduced survival only at the lowest temperature. Moreover, the lowest temperature reduced the development rate of all stages. The impact of light conditions was less pronounced and more variable: constant light reduced the survival of nymphs I at lower temperatures, but increased that of larvae. Moreover, light increased the time of embryonic development and duration of nymphal stages, particularly at lower temperatures (12-22°C). Thus, the most optimal locations for spiders seem to be dark (though except larval stage) and warm (25°C) sites, where their development is fastest and mortality lowest.

Changes of the phytoplankton community as symptoms of deterioration of water quality in a shallow lake.

Covering more than 60% of the lake surface, macrophytes determined the taxonomic composition of phytoplankton. We have found numerous indications of ecological deterioration and an increased trophic level year to year: an increased total number of taxa; a significantly increased number of species of Chlorophyta, Bacillariophyceae and Cyanoprokaryota; a decreased number of Chrysophyceae; increased Nygaard index, and high diversity and variability of phytoplankton functional groups. Within 2 years (2002 and 2003) algal biomass doubled: from 3.616 to 7.968 mg l-1. An increased contribution of Chlorococcales and Cyanoprokaryota indicates progressive eutrophication of the lake. The average size of planktonic algae increased, particularly Cyanoprokaryota, where small-celled decreased dramatically and were replaced by large colonies. Cyanoprokaryota remained the dominant group of phytoplankton after 10 years, and the ecosystem of the lake remained in the turbid state. This group of algae had the average biomass 9.734 mg l-1, which constituted almost 92% of the total biomass.

Bicephality, a seldom occurring developmental deformity in Tegenaria atrica caused by alternating temperatures.

The experiment was aimed at demonstrating the relationship between deformities of the front part of the prosoma accompanied by changes in the brain structure in bicephalous Tegenaria atrica and exposure of their embryos to temperature fluctuations. By exposing spider embryos to alternating temperatures of 14 and 32°C for the first 10 days of embryonic development, we obtained eight two-headed individuals, subsequently divided into three groups according to morphological differences. We described in detail morphological abnormalities of the prosoma identified in members of each group. Histological examination confirmed a close relationship between morphological deformities and the brain structure of teratogenically changed spiders. The fusion of appendages (pedipalps and chalicerae) was accompanied by the fusion of corresponding ganglia. The absence of appendages (pedipalps) was accompanied by the absence of corresponding ganglia. This correlation may have resulted from previously impaired neuromere development which led to changes in the morphological structure of the prosoma. Since no deformities were identified in control animals, it can be concluded that bicephaly was caused by exposing embryos to alternating temperatures.

Teratological deformities of pedipalps in the Tegenaria atrica spider, induced by low and high temperatures applied alternately.

The study was aimed at demonstrating the relationship between temperature (as a factor which disturbs morphogenesis) and deformities in the front part of the prosoma in Tegenaria atrica. By exposing spider embryos to alternating temperatures of 14 and 32°C for the first 10 days of embryonic development, i.e. until the first metameres of the prosoma appeared on the germ band, we obtained individuals with a range of anomalies including those which affected the prosomal morphology. We selected five spiders with deformities of pedipalps or of pedipalps and walking legs for comprehensive analysis. The results indicate a relationship between temperature applied as a teratogenic factor and anomalies in the front part of the prosoma.

Morphometric Changes of the Central Nervous System of Oligomelic Tegenaria atrica Spiders.

Oligomely is an anomaly manifested in the morphology of spiders (except for deformations of the prosoma and exoskeleton), by the absence of one or more appendages, and in their anatomy by the absence of neuromeres. This study was aimed at determining whether there is a correlation between the absence of a neuromere or its half in the subesophageal ganglia and the volume of the prosoma. Morphometric studies involved oligomelic specimens of Tegenaria atrica with the absence of one walking leg and two walking legs. Volumetric analysis concerned with nymph stage II of spiders obtained after exposing the embryos to alternating temperatures of 14 and 320C. The results were compared with those obtained from the histological analysis of the prosoma and central nervous system of control individuals. It was found that there was no relationship between the absence of half or an entire neuromere and the volume of the prosoma of oligomelic specimens. The volume of the central nervous system decreased but the volume change was not proportional to the changes in the prosoma volume. During studies, it was found that the lack of neuromeres resulted in an increase in the volume of remaining neuromeres.

Morphological and anatomical changes related to leg anomalies in Tegenaria atrica.

A range of leg anomalies was detected in embryos of the Tegenaria atrica spiders exposed to alternating temperatures of 14 and 32 °C. Multiple anomalies were observed in 13 individuals. This study is based on five individuals: two individuals affected by oligomely combined, respectively, with heterosymely and polymely, one affected by polymely with heterosymely, one by complicated polymely (accompanied by the reduction in length and malformations of the distal parts of the legs), and one individual with pure polymely. Changes in the central nervous system of these five individuals were described in detail on the basis of histological sections. The changes were mainly related to the number of neuromeres. Individuals affected by polymely had additional ganglia corresponding to the number of additional appendages, whereas the absence of a leg (oligomely) was associated with the absence of a ganglion. Histological analysis showed the fusion of ganglia in the three polymelic specimens, even though additional appendages were not fused.

The central nervous system of heterosymelic individuals of the spider Tegenaria atrica.

This paper presents the results of research on the nervous system in individuals of Tegenaria atrica with heterosymely of walking legs, a pedipalp and the first walking leg. Temperatures alternating between 14 degrees and 32 degrees C every 12 hours were applied as a teratogenic factor in the early stage of embryogenesis. From the thus obtained specimens, histological sections were taken using the paraffin method and then stained. Analysis of the nervous system in individuals with partial heterosymely of walking legs showed no significant changes in the structure of subesophageal nervous mass. In most of the studied individuals with partial and total heterosymely of a pedipalp and walking leg no changes were observed in the relevant parts of the nervous system either, although in two cases a fusion of nerve ganglia was noted, from which the nerves branched off towards the conjoined legs.