Texas brown tarantula, Aphonopelma hentzi.
Although both have evolved from a segmented ancestor, as can still be seen in the larvae of insects, spiders and mites differ from insects in the number of major body-parts. While insects have well-defines head, thorax (to which wings and legs are attached) and an abdomen, where the reproductive organs or normally located, spiders, scorpions, tics and mites (arachnids or chelicerates) have just two - a cephalothorax, combining the head and thorax, and an abdomen.
Now scientists have discovered a gene in the chelicerates that controls the development of the 'waist' between the cephalothorax and the abdomen, which is missing in insects. The loss of this gene could be the reason the two groups of arthropods evolved in different directions.
The team of scientists, led by Emily V. W. Shetton, of the Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, USA, have just published their findings, open access, in PLOS Biology and explained it in a press release reprinted in Science Daily:
The research team also included: Jesús A. Ballesteros of the Department of Biology, Kean University, Union, New Jersey, USA and Pola O. Blaszczyk, Benjamin C. Klementz, and Prashant P. Sharma all of Department of Integrative Biology, University of Wisconsin-Madison.
Can you translate this abstract from a science paper into plain English, complete with a glossary? Plain English Translation:The abstract, reprinted after the press release, is rather technical so I have an AI translation in plain English, complete with a glossary of technical terms (see the panel on the right):
The body structure of chelicerates (a group of arthropods that includes spiders, scorpions, and mites) is unique compared to other arthropods because it is divided into two main parts: the front part (called the prosoma or “cephalothorax”) and the back part (called the opisthosoma or “abdomen”). However, not much is known about the genetic processes that create the dividing line between these two parts.
To learn more about these genetic processes, we developed detailed genomic data for a large spider species named Aphonopelma hentzi. We examined specific areas along the front-to-back axis of developing spider embryos and used special gene analysis methods to find potential genes that control the identity of these regions. After identifying candidate genes that were highly active in either the front or the back part, we tested their functions in a well-studied spider species, Parasteatoda tepidariorum.
We discovered that a specific gene, similar to a group of genes known as the Iroquois complex in other arthropods, is crucial for forming the boundary between the front and back body parts of spiders. This gene had not been studied before in arthropods because it was lost in the common ancestor of insects and crustaceans, making it impossible to study in commonly used insect models like fruit flies.
When we reduced the activity of this gene, which we named "waist-less," in the spider P. tepidariorum, the embryos developed with defects at the boundary between the front and back parts, leading to broken or incomplete body segments. Our study shows that the "waist-less" gene is essential for properly defining the segments at the boundary, which in adult spiders is where the narrow connection, called the pedicel, forms. These findings highlight the importance of an old, specific gene in forming the distinct body regions that define chelicerates.
Glossary:
- Chelicerate: A group of arthropods that includes spiders, scorpions, mites, and ticks.
- Arthropods: A large group of invertebrate animals with exoskeletons, segmented bodies, and jointed limbs, including insects, spiders, and crustaceans.
- Tagmata (singular: tagma): Distinct body regions in arthropods. In chelicerates, these are the prosoma and opisthosoma.
- Prosoma (“cephalothorax”): The front part of a chelicerate’s body that contains the head and thorax together.
- Opisthosoma (“abdomen”): The rear part of a chelicerate’s body, behind the prosoma.
- Genomic resources: Data and tools related to the genetic material (DNA) of an organism.
- Antero-posterior axis: The front-to-back line of an organism’s body.
- Differential gene expression analyses: Techniques used to identify which genes are more or less active in different parts of an organism or under different conditions.
- Putative regulators: Genes or molecules that are believed to control certain biological processes but have not yet been definitively proven to do so.
- Bioinformatic screening: The use of computer-based tools to analyze biological data, such as gene sequences, to find potential candidates for further study.
- Homeobox genes: A group of genes that control the development of the body's layout and structures.
- Homolog: A gene related to another gene in different species due to shared ancestry.
- Pancrustacea: A group that includes insects and crustaceans.
- Knockdown: A genetic technique used to reduce the expression of a specific gene to study its function.
- Germ bands: Early developmental structures in arthropod embryos that give rise to the body segments.
- Pedicel: A narrow, waist-like structure in spiders that connects the prosoma and opisthosoma.
- Paralog: A gene related to another gene in the same organism, usually due to a duplication event in the genome.
- Taxon-restricted: Refers to genes or traits that are specific to a particular group of organisms.
Ancient gene gives spiders their narrow waistFor plain English translation of the following abstract, see the AI panel on the right:
Sequencing and gene silencing revealed a previously unstudied gene that regulates spider development
An ancient gene is crucial for the development of the distinctive waist that divides the spider body plan in two, according to a study publishing August 29th in the open-access journal PLOS Biology by Emily Setton from the University of Wisconsin-Madison, US, and colleagues.
The spider body is divided into two sections, separated by a narrow waist. Compared to insects and crustaceans, relatively little is known about embryonic development in spiders, and the genes involved in the formation of the spider waist are poorly understood.
To investigate, researchers sequenced genes expressed in embryos of the Texas brown tarantula (Aphonopelma hentzi) at different stages of development. They identified 12 genes that are expressed at different levels in embryonic cells on either side of the waist. They silenced each of these candidate genes, one by one, in embryos of the common house spider (Parasteatoda tepidariorum) to understand their function in development. This revealed one gene -- which the authors named 'waist-less' -- that is required for the development of the spider waist. It is part of a family of genes called 'Iroquois', which have previously been studied in insects and vertebrates. However, an analysis of the evolutionary history of the Iroquois family suggests that waist-less was lost in the common ancestor of insects and crustaceans. This might explain why waist-less had not been studied previously, because research has tended to focus on insect and crustacean model organisms that lack the gene.
The results demonstrate that an ancient, but previously unstudied gene is critical for the development of the boundary between the front and rear body sections, which is a defining characteristic of chelicerates -- the group that includes spiders and mites. Further research is needed to understand the role of waist-less in other chelicerates, such as scorpions and harvestman, the authors say.
The authors add, "Our work identified a new and unexpected gene involved in patterning the iconic spider body plan. More broadly, this work highlights the function of new genes in ancient groups of animals."
An ancient gene is crucial for the development of the distinctive waist that divides the spider body plan in two, according to a study publishing August 29th in the open-access journal PLOS Biology by Emily Setton from the University of Wisconsin-Madison, US, and colleagues.
The spider body is divided into two sections, separated by a narrow waist. Compared to insects and crustaceans, relatively little is known about embryonic development in spiders, and the genes involved in the formation of the spider waist are poorly understood.
To investigate, researchers sequenced genes expressed in embryos of the Texas brown tarantula (Aphonopelma hentzi) at different stages of development. They identified 12 genes that are expressed at different levels in embryonic cells on either side of the waist. They silenced each of these candidate genes, one by one, in embryos of the common house spider (Parasteatoda tepidariorum) to understand their function in development. This revealed one gene -- which the authors named 'waist-less' -- that is required for the development of the spider waist. It is part of a family of genes called 'Iroquois', which have previously been studied in insects and vertebrates. However, an analysis of the evolutionary history of the Iroquois family suggests that waist-less was lost in the common ancestor of insects and crustaceans. This might explain why waist-less had not been studied previously, because research has tended to focus on insect and crustacean model organisms that lack the gene.
The results demonstrate that an ancient, but previously unstudied gene is critical for the development of the boundary between the front and rear body sections, which is a defining characteristic of chelicerates -- the group that includes spiders and mites. Further research is needed to understand the role of waist-less in other chelicerates, such as scorpions and harvestman, the authors say.
The authors add, "Our work identified a new and unexpected gene involved in patterning the iconic spider body plan. More broadly, this work highlights the function of new genes in ancient groups of animals."
AbstractCreationists prefer to believe that spiders and insects haven't evolved over millions of years, the way this sort of scientific evidence shows, but were created by magic out of dirt just a few thousand years ago because their mummy and daddy said so. It's virtually certain that their mummy and daddy had no education in biology, or they would have known better.
The chelicerate body plan is distinguished from other arthropod groups by its division of segments into 2 tagmata: the anterior prosoma (“cephalothorax”) and the posterior opisthosoma (“abdomen”). Little is understood about the genetic mechanisms that establish the prosomal-opisthosomal (PO) boundary. To discover these mechanisms, we created high-quality genomic resources for the large-bodied spider Aphonopelma hentzi. We sequenced specific territories along the antero-posterior axis of developing embryos and applied differential gene expression analyses to identify putative regulators of regional identity. After bioinformatic screening for candidate genes that were consistently highly expressed in only 1 tagma (either the prosoma or the opisthosoma), we validated the function of highly ranked candidates in the tractable spider model Parasteatoda tepidariorum. Here, we show that an arthropod homolog of the Iroquois complex of homeobox genes is required for proper formation of the boundary between arachnid tagmata. The function of this homolog had not been previously characterized, because it was lost in the common ancestor of Pancrustacea, precluding its investigation in well-studied insect model organisms. Knockdown of the spider copy of this gene, which we designate as waist-less, in P. tepidariorum resulted in embryos with defects in the PO boundary, incurring discontinuous spider germ bands. We show that waist-less is required for proper specification of the segments that span the prosoma-opisthosoma boundary, which in adult spiders corresponds to the narrowed pedicel. Our results demonstrate the requirement of an ancient, taxon-restricted paralog for the establishment of the tagmatic boundary that defines Chelicerata.
Introduction
Functional understanding of the evolution of animal body plans is frequently constrained by 2 bottlenecks. First, developmental genetic datasets and functional toolkits are often asymmetrically weighted in favor of lineages that harbor model organisms, to the detriment of phylogenetically significant non-model groups. Second, models of ontogenetic processes that are grounded in model systems vary in their explanatory power across diverse taxa, both as a function of phylogenetic distance, as well as the evolutionary lability of different gene regulatory networks (GRNs) [1–4]. In Arthropoda, understanding of morphogenesis, as well as the evolutionary dynamics of underlying GRNs, is largely grounded in hexapod models and, particularly, holometabolous insects. Candidate gene approaches derived from studies of insect developmental genetics have thus played an outsized role in understanding the mechanisms of arthropod evolution, with emphasis on processes like segmentation, limb axis patterning, and neurogenesis [5–10]. However, the candidate gene framework has its limits in investigations of taxon-specific structures (e.g., spider spinnerets, sea spider ovigers) [11–13], or when homologous genes or processes do not occur in non-model taxa (e.g., bicoid in head segmentation) [7,14].
These limits are accentuated in Chelicerata (e.g., spiders, scorpions, mites, horseshoe crabs), the sister group to the remaining arthropods. The bauplan of most chelicerates consists of 2 tagmata, the anterior prosoma (which bears the eyes, mouthparts, and walking legs) and the posterior opisthosoma (the analog of the insect abdomen). Even at this basic level of body plan organization, differences in architectures are markedly evident between chelicerates and the better-studied hexapods. The chelicerate prosoma typically has 7 segments and includes all mouthparts and walking legs, whereas the insect head has 6 segments and bears only the sensory (antenna) and gnathal appendages (mandible, maxilla, labium); locomotory appendages of insects occur on a separate tagma, the thorax [15].
Comparatively little is known about how these functional groups of segments are established in chelicerates, by comparison to their insect counterparts. Due to the phylogenetic distance between hexapods and chelicerates, homologs of insect candidate genes that play a role in tagmosis can exhibit dissimilar expression patterns or incomparable phenotypic spectra in gene silencing experiments in spiders, a group that includes the leading models for study of chelicerate development [13,14,16–18]. A further complication is the incidence of waves of whole genome duplications (WGDs) in certain subsets of chelicerate orders, such as Arachnopulmonata, a group of 6 chelicerate orders that includes spiders [19–22]. The retention of numerous paralogous copies that diverged prior to the Silurian represents fertile ground for understanding evolution after gene duplication but also presents the potential barrier of functional redundancy or replacement between gene copies. Accordingly, there are few functional datasets supporting a role for lineage-specific gene duplicates in the patterning of arachnid body plans [23,24].
To advance the understanding of chelicerate body plan patterning and address possible roles for retained paralogs in chelicerate tagmosis, we generated transcriptional profiles of prosomal and opisthosomal tissues of a large-bodied spider (a tarantula), across developmental stages pertinent to posterior patterning. We applied differential gene expression (DGE) analyses to identify taxon-specific gene duplicates that were differentially expressed across the prosomal-opisthosomal (PO) boundary and screened candidates using an RNA interference (RNAi) gene silencing approach. Through this approach, we were able to identify one of the 5 spider homologs of Iroquois (Iroquois4 sensu [25]; Iroquois3-2, sensu [26]) as playing a role in patterning the segments spanning the PO boundary. Our results provide a functional link between an unexplored gene copy restricted to non-pancrustacean arthropods and the boundary between the tagmata of chelicerates.
Setton EVW, Ballesteros JA, Blaszczyk PO, Klementz BC, Sharma PP (2024)
A taxon-restricted duplicate of Iroquois3 is required for patterning the spider waist. PLoS Biol 22(8): e3002771. https://doi.org/10.1371/journal.pbio.3002771
Copyright: © 2024 The authors.
Published by PLoS. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Tarantulas are living fossils, existing anywhere from 120 million years ago in the Cretaceous period, Mesozoic era, to 400 million years or more in the Devonian period, Paleozoic era. They existed with Trilobites and Dinosaurs, and they existed during the Tertiary period to the present day. They have been around many, many times longer than 10,000 years.
ReplyDeleteThe Goliath Tarantula is one of the largest at 12 inches long and a quarter pound in weight, or 4 ounces. The venom isn't lethal to humans but it can kill any small animal, and the large powerful fangs can pierce human fingernals.
Many species of Tarantulas are bad tempered, especially from Africa, Asia, Indonesia, and Australia. The most aggressive New World species is Phormictopus Cancerides, or the Haitian Brown Tarantula from Haiti and the Dominican Republic and Brazil. It's bite is anywhere from moderately to intensel local pain, headache, nausea, fever, and itching for humans, and it can kill any small animal. They have been known to strike the glass in their containers with their fangs, and there's a video of a specimen in the Dominican Republic coming out of a bush to attack a car full of tourists. It was an ernomous specimen and seems to be at least 12 inches long. These are normally highly aggressive animals.
Tarantulas with potent venoms are Poecilotheria from India, Stromatopelma from Africa, Haplopelma from Asia, and Selenocosmia from Australia. Bites from these Old World species cause intense local pain, nausea, vomiting, muscular cramps and spasms to human victims. The Orange Baboon Tarantula of Africa has bite more painful than childbirth according to a female victim who was bitten.
Even the species with weak venoms such as the Chilean Rose Tarantula of the genus Grammostola, the Mexican Redknee Tarantula of the genus Brachypelma, and the Aphonopelma Hentzi have venoms that can kill mice but are not deadly to humans. Tarantulas have evolved venoms to kill small animals but not to kill adult humans.
If one wishes to sometimes hold a Tarantula the one with the calmest temperament is the Eauthlus species Red, or Chilean Dwarf Flame Tarantula, and the Pink Zebra Beauty Tarantula of South America. All the other species are either too aggressive or very unpredictable. Actually all are unpredictable in temperament.
People are keeping and breeding Tarantulas of many species, and holding them, resulting in more bite reports. These animals are truly venomous, so they shouldn't be handled often. While the venom can't kill an adult human it could conceivably kill a human baby if it's an Old World species, and small animals of all kinds will die from Tarantula venom, and the hairs from New World species can cause irritation if it gets in the eyes, nose, mouth, and ears. These animals are best left to just look at and not touch.