Anna L. M. Macagno

Publications

• 1.79

  Impact points

  Trade-off between horns and other functional traits in two Onthophagus species (Scarabaeidae, Coleoptera)

  Pizzo A, Macagno A.L.M, Dusini S, Palestrini C

  Zeitschrift für Morphologie der Tiere. 01/2012; 131(1):57-68.

  Beetle horns are extraordinarily diversified secondary sexual structures used for mate choice and male–male combat. Due to an interaction of nutritional, hormonal and genetic factors, their polyphenic development is metabolically expensive and occurs in the virtually closed system of the pre-pupal s... [more] Beetle horns are extraordinarily diversified secondary sexual structures used for mate choice and male–male combat. Due to an interaction of nutritional, hormonal and genetic factors, their polyphenic development is metabolically expensive and occurs in the virtually closed system of the pre-pupal stage, after the developing larva has stopped feeding. Previous studies showed the occurrence of resource competition resulting in a trade-offs between horns and other morphological structures. These studies also revealed functional associations between autoecology and horns, as a function of their physical location (i.e. head versus pronotum), and suggested that constraints imposed by trade-offs on adult morphology may have profound evolutionary consequences, such as ecological and reproductive isolation. In this study, we compared tradeoff patterns between horns and other functional traits (eyes, antennae, legs, head, epipharynges and genitalia) in two congeneric species bearing horns located in the same anatomical area, but with different morphologies. Specifically, we considered Onthophagus taurus, characterised by a pair of long, lunated cephalic horns, and Onthophagus fracticornis, expressing a single cephalic horn. We demonstrated that, even when horns are located in the same physical position on the insect’s body, differences in horn morphology can bring about differences in how functional traits respond to horn investment. These differences are interpretable in the light of the hierarchy of functions carried out by these structures and their component parts in each species.
• 4.41

  Impact points

  Shape - but not size - codivergence between male and female copulatory structures in Onthophagus beetles

  Macagno A.L.M., Pizzo A., Parzer H.F., Palestrini C., Rolando A., Moczek A.P.

  PLoS ONE. 01/2011; 6:e28893.

  Genitalia are among the fastest evolving morphological traits in arthropods. Among the many hypotheses aimed at explaining this observation, some explicitly or implicitly predict concomitant male and female changes of genital traits that interact during copulation (i.e., lock and key, sexual conflic... [more] Genitalia are among the fastest evolving morphological traits in arthropods. Among the many hypotheses aimed at explaining this observation, some explicitly or implicitly predict concomitant male and female changes of genital traits that interact during copulation (i.e., lock and key, sexual conflict, cryptic female choice and pleiotropy). Testing these hypotheses requires insights into whether male and female copulatory structures that physically interact during mating also affect each other's evolution and patterns of diversification. Here we compare and contrast size and shape evolution of male and female structures that are known to interact tightly during copulation using two model systems: (a) the sister species O. taurus (1 native, 3 recently established populations) and O. illyricus, and (b) the species-complex O. fracticornis-similis-opacicollis. Partial Least Squares analyses indicated very little to no correlation between size and shape of copulatory structures, both in males and females. Accordingly, comparing shape and size diversification patterns of genitalia within each sex showed that the two components diversify readily - though largely independently of each other - within and between species. Similarly, comparing patterns of divergence across sexes showed that relative sizes of male and female copulatory organs diversify largely independent of each other. However, performing this analysis for genital shape revealed a signature of parallel divergence. Our results therefore suggest that male and female copulatory structures that are linked mechanically during copulation may diverge in concert with respect to their shapes. Furthermore, our results suggest that genital divergence in general, and co-divergence of male and female genital shape in particular, can evolve over an extraordinarily short time frame. Results are discussed in the framework of the hypotheses that assume or predict concomitant evolutionary changes in male and female copulatory organs.

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• Size and shape interspecific divergence patterns partly reflect phylogeny in an Onthophagus species-complex (Coleoptera: Scarabaeidae)

  Macagno A.L.M., Pizzo A., Rolando A., Palestrini C.

  Zoological Journal of the Linnean Society. 01/2011; 162:482-498.

  Polyphenism has been suggested as an accelerator for morphological evolution and speciation. In the dung beetles of the genus Onthophagus, horn expression is polyphenic: large males develop horns whereas smaller males express greatly reduced or no horns. Horn static allometries seem to diverge rapid... [more] Polyphenism has been suggested as an accelerator for morphological evolution and speciation. In the dung beetles of the genus Onthophagus, horn expression is polyphenic: large males develop horns whereas smaller males express greatly reduced or no horns. Horn static allometries seem to diverge rapidly amongst extant taxa, a process which might trigger changes in the male genital morphology, thus possibly promoting speciation as a by-product. It can therefore be hypothesized that interspecific distances in allometries and, possibly, in other morphological traits mirror phylogenetic distances. In this study we first assessed the phylogenetic relationships amongst three closely related taxa belonging to the so-called ‘Onthophagus fracticornis-similis-opacicollis’ species-complex by sequencing the mitochondrial gene cytochrome oxidase subunit 1 (cox1). Biomolecular results indicated three independent lineages, the closest relationships being found between Onthophagus similis and Onthophagus opacicollis. Then we assessed the extent to which divergence pattern of horn static allometries and size and shape divergence patterns of one genital (paramere) and two nongenital (head and epipharynx) structures mirrored the phylogenetic relationships. Interspecific divergence patterns of horn static allometries, paramere, and head shape were found to be congruent with the evolutionary relationships inferred from biomolecular data. Nevertheless, paramere size and epipharynx shape showed patterns not consistent with the phylogeny. Furthermore, the relative size of nongenital structures showed little interspecific divergence compared to their shapes. Our results suggest that size and shape interspecific divergence mirror phylogeny only in part; they also indicate that distinct morphological traits may differ in their tendency to evolve in concert, and that size and shape of the same trait can evolve independently across species.

• Seasonal constraints on the mandible allometry of Lucanus cervus (Coleoptera: Lucanidae)

  Hardersen S., Macagno A.L.M., Sacchi R., Toni I.

  European Journal of Entomology. 01/2011; 108:461-468.

  In insects, allometries of exaggerated traits such as horns or mandibles are often considered species specific and constant during a season. However, given that constraints imposed by the advancing season affect the developmental processes of organisms, these allometries may not be fixed, and the sw... [more] In insects, allometries of exaggerated traits such as horns or mandibles are often considered species specific and constant during a season. However, given that constraints imposed by the advancing season affect the developmental processes of organisms, these allometries may not be fixed, and the switch point between morphs may vary between populations and within populations during a season. The hypothesis of such a seasonal variation in exaggerated traits was tested using the dimorphic males of the beetle Lucanus cervus. The remains of specimens killed by predators were collected along forest tracks from mid May to late August 2008 in a protected lowland forest in northern Italy. The largest beetles were collected in mid May and average size thereafter decreased. Males collected early in the season mostly had large mandibles (i.e. they belonged to the major morph). In contrast, late in the season the probability of finding males with large mandibles was very low. The threshold body size determining morph expression also shifted during the season. Early in the season, the threshold pronotum width for a 50% chance of developing into the major morph was 1.74 cm, whereas later in the season it was 1.90 cm. This shift in the threshold body size was interpreted as the effect of phenotypic plasticity in a population exposed to constraints imposed by the advancing season.

• Epipharynx shape as a tool to reveal differentiation patterns between insect sister species: insights from Onthophagus taurus and O. illyricus (Insecta: Coleoptera: Scarabaeidae)

  Pizzo A., Macagno A.L.M., Roggero A., Rolando A., Palestrini C.

  Organisms Diversity & Evolution. 01/2009; 9:189-200.

  We evaluated the potential of the adult epipharynx to reveal interspecific differentiation patterns in closely related Onthophagus species. Although easy to analyse, this structure has received little attention in Scarabaeidae taxonomy, probably because a qualitative inspection of its shape often do... [more] We evaluated the potential of the adult epipharynx to reveal interspecific differentiation patterns in closely related Onthophagus species. Although easy to analyse, this structure has received little attention in Scarabaeidae taxonomy, probably because a qualitative inspection of its shape often does not yield differences between congeneric species. The polyphenic sister species Onthophagus taurus Schreber, 1759 and O. illyricus Scopoli, 1763 were chosen as a case study. They are extremely similar, to the extent that in some cases they cannot be identified unambiguously without the help of biomolecular analysis. In this study, a combination of linear measurements and a landmark-based approach was employed to quantify inter- and intraspecific shape variation in the epipharynx of specimens sampled at the same study site. Our results showed that the epipharynx is a monomorphic structure: its shape does not vary as a function of sex or male phenotype. In males, epipharynx shape does not change with head shape or horn length. The close proximity of the epipharynx to the horns and the synchronous developmental patterns of these two structures suggest that a developmental trade-off may act between them. Despite these predisposing conditions, however, our results suggest that epipharynx size is not subject to costs associated with horn development, and that the trait is highly canalised. Surprisingly, when using geometric morphometrics the epipharynx appears to be a better tool than genitalia for discriminating between the two sister species.

• The maintenance of extensively exploited pastures within the Alpine mountain belt: implications for dung beetle conservation (Coleoptera: Scarabaeoidea)

  Macagno A.L.M., Palestrini C.

  Biodiversity and Conservation. 01/2009; 18:3309-3323.

  The abandonment of marginal areas and the decline of traditional small-scale cattle-breeding is bringing about substantial changes in many areas of the Alpine mountain belt. Extensively exploited pastures, which were colonized by typical ecological communities, are now being replaced by shrublands a... [more] The abandonment of marginal areas and the decline of traditional small-scale cattle-breeding is bringing about substantial changes in many areas of the Alpine mountain belt. Extensively exploited pastures, which were colonized by typical ecological communities, are now being replaced by shrublands and forests. In this paper, we evaluate the effectiveness of the maintenance of small pastures for dung beetle (Scarabaeoidea: Geotrupidae, Aphodiidae, Scarabaeidae) conservation in a protected area of the north-western Italian Alps. From July until September 2007, we studied the dung beetle coenosis in the main habitats of the mountain belt: beech forest, scots pine forest, mountain pine forest and pasture. Twenty-three species were sampled. We compared abundance, species richness, a-diversity, evenness and species turnover between the four habitat assemblages and performed a correspondence analysis based on dominance patterns of the three families. Two main ensembles were identified: a pasture ensemble, highly diverse and dominated by Scarabaeidae, and a closed habitats ensemble, less structured and dominated by Aphodiidae and Geotrupidae. Combining habitat specificity and fidelity, the IndVal method showed that half of the species collected made a strong habitat selection toward pasture, while only C. granarius (Aphodiidae) was a reliable indicator of woody areas. We therefore conclude that the loss of extensively exploited pastures may bring about fundamental changes in dung insect communities. In protected areas, a management policy intended to preserve the traditional, sustainable human activities within the mountain belt is highly recommended for the conservation of these insects.

• Horn polyphenism and related head shape variation in a single-horned dung beetle: Onthophagus (Palaeonthophagus) fracticornis (Preyssler, 1790) (Coleoptera: Scarabaeidae)

  Macagno A.L.M., Pizzo A., Roggero A., Rolando A., Palestrini C.

  Journal of Zoological Systematics and Evolutionary Research. 01/2009; 47:96-102.

  Horns of Onthophagus beetles are typical examples of phenotypically plastic traits: they are expressed as a function of environmental (nutritional) stimuli, and their reaction norm (i.e. the full set of horn lengths expressed as a response to different degrees of nutritional states) can be either li... [more] Horns of Onthophagus beetles are typical examples of phenotypically plastic traits: they are expressed as a function of environmental (nutritional) stimuli, and their reaction norm (i.e. the full set of horn lengths expressed as a response to different degrees of nutritional states) can be either linear or threshold-dependent. Horned males of Onthophagus (Palaeonthophagus) fracticornis (Preyssler, 1790) bear a single triangular cephalic protrusion of vertex carina, which has received phylogenetic support as the most primitive horn shape in the genus. Inter- and intra-sexual patterns of horn expression were studied in O. fracticornis by means of static allometries while associated variations in head shape were assessed using geometric morphometric techniques. The relation between log-transformed measurements of body size and vertex carina supported an isometric scaling in females. On the contrary, a sigmoidal model described better the horn length-body size allometry in males, with a switch point between alternative morphs at a pronotum width of 3.88 mm. Sigmoidal static allometries of horns in Onthophagus populations arise from a threshold-dependent developmental process of horn growth. This process underlies the expression of both plesiomorphic and apomorphic horn shapes in the genus. Given that the single-horn model has been identified as primitive, we propose that such a developmental process giving rise to it may be evolutionarily ancient as well. Horn expression was accompanied by a deformation of the head which makes minor and major morphs appear even more different. Therefore, in this species both horn and head shape expression contribute to male dimorphism.

• Movement and demographics of Libellula fulva (Odonata, Libellulidae)

  Macagno A.L.M., Boano G., Palestrini C., Stassi M., Rolando A.

  Environmental Entomology. 01/2008; 37:1145-1153.

  Many capture-recapture studies on adult dragonflies have found male-biased sex ratios. However, few have estimated survivorship of males and females separately from data on frequency of recaptures in the field. Even when daily survival and capture probabilities are estimated separately, controversie... [more] Many capture-recapture studies on adult dragonflies have found male-biased sex ratios. However, few have estimated survivorship of males and females separately from data on frequency of recaptures in the field. Even when daily survival and capture probabilities are estimated separately, controversies can arise on whether sex biases in local survival are to be attributed to mortality or permanent emigration from the study site. The knowledge of male and female movements, assessed on an appropriate scale (i.e., within and outside the breeding site), can help address this issue. In this paper, we performed a 4-yr capture-recapture study of two Libellula fulva Muller populations in northwest Italy. Cormack-Jolly-Seber models were used to get unbiased estimates of demographic parameters (daily survival and capture probabilities, sex ratio, mean life span, and population size). Movement parameters were measured directly by georeferencing encounters. Moderate differences insurvival, with males surviving better than females,were found in one population and not in the other, suggesting that these differences are not an inherent characteristic of the species. In the population with lower female survival, females were not more vagile than males, thus indicating their lower survival was caused by actual mortality rather than to emigration. In the population with no survival differences between males and females,marked males outnumbered females, but estimated sex ratios were 1:1 or female biased. Therefore, raw field data were misleading because they led to underestimates of the more elusive sex and overestimates of the more detectable one (males). Survival and movement differences detected in the two populations are discussed in the framework of local environmental and demographic factors.