The widow spider family, also scientifically known as Latrodectus, is mainly identified by its shiny black body and the red area located on its belly. These spiders are poisonous and tend to cause injury when a bite occurs. Home to the Southern and Western parts of the United States, they are also found in barns, stone walls, and anything made of wood. This paper by Lui et al researches the early development of the anterior body region of the grey widow spider.
This species has a specific body tagmosis* that isn’t found in any other euarthropods* which includes: the “prosoma”* anterior region that contains seven sections and the “opisthosoma”* posterior region that contains thirteen. Because of this it provided them with the perfect opportunity to research the developing morphology and topology of structures of the anterior region of the embryos across arthropods.
Based on previous research, we are able to summarize the embryonic development of spiders. After cleavage is finished, the spider eggs go into a blastula stage where majority of the blastoderm eggs accumulate on one side. Another accumulation of eggs underneath the center of the germ disc forms the caudal cumulus. The caudal cumulus finally breaks away splitting the germ disc into two parts creating a germinal band. Inversion is now beginning. Inversion within a spider is when the germ band splits in two and eventually forms an epidermal layer on the dorsal side of the egg. This is called “dorsal closure”.
Need to know terms:
*tagmosis- The evolutionary process that creates tagmata by fusing and modifying segments is called tagmosis
*euarthropods- trilobites, crustaceans, myriapods and insects
*prosoma- a fused head and thorax
*opisthosoma- the abdomen
*blastula- an animal embryo at the early stage of development when it is a hollow ball of cells
Chosen because: 1. easy lab culture for the adults 2. large quantity of eggs produced by females 3. development for this species’ embryos has never been done
- Eggs were removed from cocoon ~30 min
- They were then rinsed in 90% ethanol
- The inner vitelline membrane was removed
- Dissected embryos were dehydrated through an ethanol series
- Samples were sputter-coated with a gold and palladium mixture to be observed under a scanning electron microscope (SEM)
Liu et al. 2009
Figure 1: 1A shows the spider embryo where the anterior and posterior ends of the egg come around to meet each other. 1B displays the different angles where they analyzed the embryo (anterior, median, and posterior). 1C-E are different shots of the anterior region that were analyzed from the SEM equipment.
*Abbreviations: CH: chelicerae, e: pedipalpal endite, EP: epithelial portion, HY: hypostome, L1–4: walking limbs 1–4, M: mouth opening, OLB1–4: opisthosomal limb buds 1–4, PCL: pre-cheliceral lobes, PP: pedipalp, TE: telson, VS: ventral sulcus, Y: yolk.
Liu et al. 2009
Figure 2: Additional photos of the spider embryo during steps 9-16. These are also viewed from the anterior position. A- Step 9: the lateral and median sections begin to merge together. B-Step 10: the anterior region for each lobe is seen to be more differentiated than previous pictures. C- Step 11: the widths in the lobe regions are reduced. D- Step 12: the entire lobe decreased in size and outline of the prospective prosomal shield is seen by a dashed line. E- Step 13: the ridge, which is the white arrowhead, is reduced. F- Step 14: the anterior parts of the lobes finally fuse together. G- Step 15: The holes are smaller and a labium (LB) starts to develop at the anterior part of the embryo.H- Step 16: The shield is very well developed.
Liu et al. 2009
Figure 3: Pictures A-P all represent the different steps that the embryo goes through. The different colors correspond to specific regions. Dark green – the pre-cheliceral lobes, Yellow- the marginal region & central area, Light green – the postero-median bridge which connects the lobes, Dark yellow – the furrows, Red – the mouth region, Orange – the chelicerae, Light blue – the pedipalps, Grey – the four posterior-most prosomal segments. In all of the pictures there is an arrow that marks the major structures in each.
Liu et al. 2009
Figure 4: These are SEM pictures from a recently hatched spider egg. A- a photo from the ventral view of the spider. B- a close up picture of the mouth on the same spider from picture A.
Major Findings & Conclusions:
- Each pre-cheliceral lobe has two areas: (1) a marginal region that transforms into the anterior part of the prosomal shield (2) a central area that fuses and separates from the marginal region by three furrows.
- The anterior furrow is significant for the brain formation of a spider.
- The increased distance between the hypostome and the anterior margin of the pre-cheliceral lobe suggests the mouth region changes position in ventral and posterior direction during embryonic development
- The entire shift of the mouth region from anterior to posterior belongs to the ground pattern of, at least, the Chelicerata
- The prosomal shield contains the marginal region of the previous pre-cheliceral lobe & the four posterior-most prosomal segments.
- The ventral sulcus and the inversion are basically the same structure and phenomenon
Strengths and Weaknesses of paper:
This paper was very detailed and produced a lot of data BUT, this paper was very extensive and there were a lot of other findings that could not be solidified because further comparisons are needed.
Liu, Y., Maas, A., and Waloszek, D. Early development of the anterior body region of the grey widow spider Latrodectus geometricus Koch, 1841 (Theridiidae, Araneae). Anthropod structure & development. Sep 2009. (38) 5: 401-416. http://www.sciencedirect.com/science/article/pii/S146780390900019X