Morphological and anatomical changes related to leg anomalies in Tegenaria atrica

Abstract

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.

Keywords: Central nervous system; Malformations; Spider; Teratogenic factor.

Fig. 1

a, b Tegenaria atrica larva with oligomely of a pedipalp and partial heterosymely of walking legs 1 and 2 (ventral view): 1 and 2—heterosymelic walking legs, the arrow indicates the location of a missing pedipalp, scale bar 0.14 mm, c frontal section through prosoma: p—pedipalp’s ganglion, l ₁–l ₄—ganglia of walking legs, the arrow indicates the fused midgut caeca, scale bar 0.09 mm, d, e larva of Tegenaria atrica with polymely and heterosymely of pedipalps (ventral view): 1 and 2—correct pedipalps, 3 and 4—polymelic pedipalps, scale bar 0.22 mm, f sagittal section through the anterior part of prosoma, p ₁—ganglion of pedipalp 1, p ₂—ganglion of pedipalp 2, p ₃ and p ₄—ganglia of fused polymelic pedipalps (3 and 4), scale bar 0.07 mm

Fig. 2

a, b Tegenaria atrica with the left-sided polymely of walking legs (dorsal view): 1–6—walking legs, scale bar 0.23 mm, c frontal section through prosoma with ganglia of walking legs: l ₁, l ₂, l ₃, and l _5,6, scale bar 0.12 mm; d frontal section through the suboesophageal neural mass: p—ganglia of pedipalps, l ₁, l ₂, l ₃, l ₄—ganglia of walking legs, scale bar 0.11 mm, e frontal section through the suboesophageal neural mass: l _3,4—fused ganglia of walking legs 3 and 4, scale bar 0.11 mm

Fig. 3

a, b Tegenaria atrica larva with polymely and oligomely of walking legs (ventral view), scale bar 0.22 mm, c frontal section through prosoma with ganglia of walking legs: l ₁, l ₂, l ₃, l ₄—ganglia of the first four walking legs, l _5,6—fused ganglia of the two last walking legs, scale bar 0.05 mm, d section through the suboesophageal mass with three ganglia of walking legs (l ₁–l ₃) (oligomely), scale bar 0.11 mm, e, f larva of Tegenaria atrica with polymely of walking legs (dorsal view): a–d—midgut caeca, 1–5—walking legs, scale bar 0.09 mm, g frontal section through suboesophageal neural mass: l _3,4—two connected ganglia of leg 3 (normal) and 4 (polymelic)