🔬 Complete Connectome · C. elegans Male

Male C. elegans
Connectome

The first complete wiring diagram of the adult male nervous system of Caenorhabditis elegans — 385 neurons, 83 male-specific, including the full sexually dimorphic mating circuit. Reconstructed from serial section electron microscopy and hosted by the Open Connectome Project.

Download Adjacency Matrices → Mating Circuit vs. Hermaphrodite Data Access
385
Total Neurons
83
Male-Specific Neurons
7,000+
Synaptic Connections
155
Muscles Mapped
579
Connectome Nodes

Overview

The adult male C. elegans has a larger nervous system than the hermaphrodite — 385 neurons compared to 302 — with the additional neurons concentrated in the tail and devoted primarily to mating behavior. The majority of male-specific neurons are associated with the tail ganglia and form the sexually dimorphic circuits required for copulation.

Two landmark studies define the male connectome. The Jarrell et al. 2012 (Science) paper reconstructed the posterior nervous system — the mating circuit — from serial EM sections of animal N2Y. The Cook et al. 2019 (Nature) paper extended this to the complete whole-animal connectome for both sexes, including the male head, nerve ring, and retrovesicular ganglion, from a new EM series. Together they provide the complete male wiring diagram with quantitative synapse counts.

The male graph from Cook et al. 2019 has 579 nodes — 385 neurons, 155 muscles, and 39 non-muscle end organs — with all chemical and gap junction synapses tabulated. The complete connectivity matrices are publicly available at WormWiring and via the OpenWorm Connectome Toolbox.

Four Striking Network Features (Jarrell et al. 2012)

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Short Parallel Pathways
Multiple, parallel, short synaptic pathways directly connecting sensory neurons to end organs — enabling rapid behavioral execution.
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Recurrent Connectivity
Recurrent and reciprocal connectivity among sensory neurons — allowing self-modulation and context-dependent gain control.
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Modular Substructure
Five functional modules: hermaphrodite contact response, locomotion, two posture modules, and insemination. Each maps to a discrete mating step.
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Feedforward Interneurons
Interneurons acting in feedforward loops — enabling robust, rapid selection and execution of behavioral steps based on multi-sensory input.

The Mating Circuit

The male mating circuitry contains 170 neurons (81 male-specific + 89 shared with hermaphrodite) and 64 muscles, organized into five behavioral modules. The circuit governs the entire mating behavioral sequence, from initial hermaphrodite contact to sperm transfer.

Module Behavioral Function Key Neurons Sensory Input
Contact Response Detects hermaphrodite body contact; initiates backing along hermaphrodite body to locate vulva PHC, PLN, PVY Mechanosensory (tail fan)
Locomotion Coordinates forward/backward movement during mate searching and along-body travel DVA, PCA, PCB Proprioceptive + chemosensory
Posture (1) Maintains ventral curvature during backing; positions tail for vulva recognition SPD, SPC, HOA Mechanosensory (spicules)
Posture (2) Controls dorsal-ventral positioning for spicule insertion alignment PGA, PGB, PGC Mechanosensory (body wall)
Insemination Drives spicule protraction and sperm transfer once vulva is located SPC, SPV, PCA Mechanosensory + proprioceptive
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Tail Ganglia

In addition to the ganglia shared with the hermaphrodite (lumbar, dorsorectal, pre-anal), the male tail contains two male-specific cloacal ganglia (CG). These house many of the 81 male-specific neurons driving the mating circuit.

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Head Sensory Neurons (CEM)

Four male-specific CEM sensory neurons in the head are born in the embryo and undergo programmed cell death in the hermaphrodite. Their function likely involves pheromone/odorant cues that mediate mate-seeking before physical contact.

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Polymodal Integration

Two-thirds of shared neurons show sexually dimorphic wiring patterns in the male. Most male-specific neurons are polymodal — integrating mechanosensory, proprioceptive, and chemosensory signals simultaneously.

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Shared vs. Sex-Specific

Of the 385 male neurons: 302 are shared with the hermaphrodite and 83 are male-specific. Among shared neurons, synaptic weights differ substantially between sexes, providing a basis for sex-specific behavioral outputs from common circuits.

Male vs. Hermaphrodite Connectome

Property ♂ Male ⚥ Hermaphrodite
Total neurons 385 302
Sex-specific neurons 83 (male) 8–14 (herm)
Total connectome nodes 579 460
Muscles mapped 155 132
Non-muscle end organs 39 26
Mating circuit neurons 170 (81+89) N/A (no mating circuit)
Tail ganglia 6 (incl. 2 CG) 4
Head CEM neurons 4 (survive) 4 (apoptosis)
Key reference Cook 2019 + Jarrell 2012 White 1986 + Cook 2019

Sexual Dimorphism Beyond Neuron Count

The difference between the sexes goes far beyond extra neurons. Cook et al. 2019 found that a surprising number of synapses between neurons in central pathways shared by both sexes also differ considerably in strength. Key findings:

  • Primary sex differences in vulval/uterine muscles and their motor neurons (hermaphrodite) vs. tail copulatory muscles and their circuits (male)
  • DVA interneuron reclassified as a sensory neuron in both sexes
  • SAB, SIA, SIB reclassified as motor neurons
  • AS11 and PDB (AS12) have extensive dendritic arbors in the male involved in mating circuitry
  • Amphid nerves contain synapses among sensory dendrites and RIP — first discovered in Pristionchus, now confirmed in C. elegans

Data Access

Connectivity matrices, synapse lists, and cell class data are available from multiple sources. All are open access.

Excel WormWiring Adjacency Matrices

Complete Cook et al. 2019 connectivity data (corrected July 2020). Includes chemical synapses, gap junctions, synapse lists, and cell class matrices for both sexes.

SI 5: Connectome adjacency matrices (hermaphrodite + male) SI 2: Synapse adjacency matrices SI 3: Lists of all synapses SI 4: Cell lists SI 6: Cell class lists SI 7: Cell class connectome adjacency matrices
Download from WormWiring →

Python OpenWorm Connectome Toolbox

Programmatic access to Cook 2019 male and hermaphrodite connectomes as structured Python objects. Install cect for direct data loading.

pip install cect
OpenWorm Toolbox →

Python Loading the Male Connectome

# Install: pip install cect from cect.Cook2019MaleReader import read_data # Load the male connectome conns, neuron_names = read_data() # conns is a dict with keys: 'chemical', 'electrical' # Each value is an NxN numpy array (N = number of neurons) chem = conns['chemical'] # directed; entry [i,j] = synapse count from i→j gap = conns['electrical'] # undirected; gap junction count print(f"Neurons: {len(neuron_names)}") print(f"Total chemical synapses: {int(chem.sum())}") print(f"Total gap junctions: {int(gap.sum() / 2)}") # Find male-specific neurons (not in hermaphrodite list) from cect.Cook2019HermReader import read_data as read_herm _, herm_names = read_herm() male_specific = [n for n in neuron_names if n not in herm_names] print(f"Male-specific neurons: {len(male_specific)}") print(f"Examples: {male_specific[:8]}") # Graph-theoretic analysis import networkx as nx import numpy as np G = nx.from_numpy_array(chem, create_using=nx.DiGraph) print(f"Nodes: {G.number_of_nodes()}") print(f"Edges: {G.number_of_edges()}") print(f"Clustering: {nx.average_clustering(G):.4f}")

OCP API RESTful Access via Open Connectome Project

# Male C. elegans token on OCP http://openconnecto.me/ocp/ca/male_celegans/info/ # Download connectivity data (replace with actual token) curl http://openconnecto.me/ocp/ca/male_celegans/info/ # Python via ndio import ndio.remote.neurodata as nd nd_obj = nd.NeuroData() info = nd_obj.get_token_info('male_celegans')

Research Timeline

1986 White et al. — Hermaphrodite Connectome

Complete wiring diagram of the hermaphrodite C. elegans nervous system (302 neurons). Published in Phil. Trans. Royal Society. The foundational dataset, digitized over subsequent decades.

2009 Varshney et al. — Hermaphrodite Digitized

Full digitization and curation of the White 1986 connectome, with gap junctions and additional chemical synapses. Published in PLOS Computational Biology.

2012 Jarrell et al. — Male Tail Connectome (Science)

First wiring diagram of the male posterior nervous system: 170 neurons (81 male-specific), 64 muscles, complete mating circuit. Revealed 5 functional modules and 4 circuit architecture features. Science 337:437–444.

2019 Cook et al. — Complete Male + Hermaphrodite (Nature)

Whole-animal connectomes for both sexes. Male: 385 neurons, 579 nodes. New EM series for male head. Quantitative synapse counts throughout. Nature 571:63–71. Data hosted at WormWiring.

2021 Witvliet et al. — 8 Developmental Stages (Nature)

Connectomes at 8 time points from L1 to adult hermaphrodite, revealing how the connectome grows and refines during development. Nature 596:257–261.

2025 Ongoing — Functional Connectomics

Randi et al. 2023 and Atanas et al. 2023 add whole-brain calcium imaging overlaid on the structural connectome — moving from anatomy to function for both sexes.

Key Publications

T. A. Jarrell, Y. Wang, A. E. Bloniarz, C. A. Brittin, M. Xu, J. N. Thomson, D. G. Albertson, D. H. Hall, and S. W. Emmons. The Connectome of a Decision-Making Neural Network. Science 337(6093):437–444, Jul 27 2012.

Science · 2012 · DOI: 10.1126/science.1221762 · Male tail mating circuit

S. J. Cook, T. A. Jarrell, C. A. Brittin, Y. Wang, A. E. Bloniarz, M. A. Yakovlev, K. C. Q. Nguyen, L. T-H. Tang, E. A. Bayer, J. S. Duerr, H. E. Bülow, O. Hobert, D. H. Hall, and S. W. Emmons. Whole-animal connectomes of both Caenorhabditis elegans sexes. Nature 571:63–71, Jul 3 2019.

Nature · 2019 · DOI: 10.1038/s41586-019-1352-7 · Complete male + hermaphrodite connectome

J. G. White, E. Southgate, J. N. Thomson, and S. Brenner. The Structure of the Nervous System of the Nematode Caenorhabditis elegans. Phil. Trans. Royal Soc. London B 314:1–340, 1986.

Phil. Trans. Royal Soc. B · 1986 · The original hermaphrodite wiring diagram

D. B. Chklovskii and C. Bargmann. Connectomics and the Neural Basis of Behaviour. Science 337(6093):397–398, 2012. (Perspective on Jarrell et al. 2012)

Science · 2012 · Editorial perspective on the male tail connectome