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Background <p>Burying beetles (Coleoptera: <i>Nicrophorus</i> spp.) are necrophagous insects well known for their highly developed parental care, which in many respects resembles the reproductive behaviour of birds. As in many other taxa, to avoid intense competition, different sympatric <i>Nicrophorus</i> species occupy distinct habitats and show variation in both seasonal and daily activity. Although niche partitioning is known to influence eye and head morphology in insects, this has been poorly studied in burying beetles. Because these beetles show sexual dimorphism in head size, we hypothesized that eye morphology may also differ between sexes and be linked to the morphology of other head structures.</p> Results <p>In most species, eye length increased more slowly than width, so larger individuals had relatively wider eyes; only <i>N. humator</i> was near isometry. The strongest negative allometry of eye size vs. body size occurred in <i>N. humator</i>, while <i>N. interruptus</i> and <i>N. vespilloides</i> were close to isometry. Eye aspect ratio (eye length-to-width) changed little with body size, except for notable differences in <i>N. interruptus</i>. PCA indicated that most variation reflects body size change as well. PC2 captured sex and eye–head relationships: females have consistently higher PC2 scores than males, driven by consistent sexual dimorphism in interocular distance and postocular area length. Larger eyes were associated with a smaller postocular area, distinguishing <i>N. humator</i> from other species in PC2. Eye size scales similarly in females and males. The extent of sexual dimorphism, however, depended on species and trait. It is stronger in head structures than eyes, most evident in <i>N. interruptus</i> and <i>N. vespilloides</i>, where it involves an enlarged postocular area, greater interocular distance, and positive eye-size allometry in males.</p> Conclusions <p>The main finding of our study is that burying beetle species differ in morphological scaling patterns and head shape. Variation and dimorphism are concentrated mainly in head structures other than the eyes, supporting the view of the head as a complex modular system. Compared with other head structures, scaling of the eyes appears more evolutionarily conserved, showing weaker sexual dimorphism and more stable allometric relationships. However, among the studied species, <i>N. humator</i> is distinct and its eye morphology may be linked to a nocturnal lifestyle. These findings provide a basis for future studies on the role of vision in carcass detection, competition, and parental behaviour in burying beetles.</p>

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Not all heads are the same: species- and sex-specific differences in eye and postocular area morphology of burying beetles (Nicrophorus spp.)

  • 期刊论文

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  • 发表日期：

    2026年7月29日

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  • Daria Bajerlein,
  • Julian Katzke,
  • Edward Baraniak,
  • Arkadiusz Urbański

摘要

Background

Burying beetles (Coleoptera: Nicrophorus spp.) are necrophagous insects well known for their highly developed parental care, which in many respects resembles the reproductive behaviour of birds. As in many other taxa, to avoid intense competition, different sympatric Nicrophorus species occupy distinct habitats and show variation in both seasonal and daily activity. Although niche partitioning is known to influence eye and head morphology in insects, this has been poorly studied in burying beetles. Because these beetles show sexual dimorphism in head size, we hypothesized that eye morphology may also differ between sexes and be linked to the morphology of other head structures.

Results

In most species, eye length increased more slowly than width, so larger individuals had relatively wider eyes; only N. humator was near isometry. The strongest negative allometry of eye size vs. body size occurred in N. humator, while N. interruptus and N. vespilloides were close to isometry. Eye aspect ratio (eye length-to-width) changed little with body size, except for notable differences in N. interruptus. PCA indicated that most variation reflects body size change as well. PC2 captured sex and eye–head relationships: females have consistently higher PC2 scores than males, driven by consistent sexual dimorphism in interocular distance and postocular area length. Larger eyes were associated with a smaller postocular area, distinguishing N. humator from other species in PC2. Eye size scales similarly in females and males. The extent of sexual dimorphism, however, depended on species and trait. It is stronger in head structures than eyes, most evident in N. interruptus and N. vespilloides, where it involves an enlarged postocular area, greater interocular distance, and positive eye-size allometry in males.

Conclusions

The main finding of our study is that burying beetle species differ in morphological scaling patterns and head shape. Variation and dimorphism are concentrated mainly in head structures other than the eyes, supporting the view of the head as a complex modular system. Compared with other head structures, scaling of the eyes appears more evolutionarily conserved, showing weaker sexual dimorphism and more stable allometric relationships. However, among the studied species, N. humator is distinct and its eye morphology may be linked to a nocturnal lifestyle. These findings provide a basis for future studies on the role of vision in carcass detection, competition, and parental behaviour in burying beetles.