Protandry, the earlier arrival of males to breeding areas than females, is a common pattern of sex-biased timing in many animal taxa (e.g. some insects, fish, amphibians, reptiles, birds and mammals). The adaptive significance of protandry is not fully understood and, since the 1970s, at least seven hypotheses for protandry have been proposed. We describe each of these hypotheses and summarize what is known about each. In three of these hypotheses, the relative arrival timing of males and females has no direct fitness consequences for males or females, but selection for different timing in each sex indirectly produces protandry. In the other four hypotheses, the difference between male and female timing has fitness consequences for males or females and selection directly maintains the fitness-maximizing degree of sex-biased timing. The hypotheses are not mutually exclusive, and the degree of multiple mating by males and the occurrence of male territoriality seem to determine the relative importance of each hypothesis. In order to understand the adaptive significance of sex-biased timing, future studies need to consider all the alternatives and to assess the costs and benefits to males of early arrival relative to calendar date, to other males and to females.

https://www.sfu.ca/biology/wildberg/NewCWEPage/papers/MorbeyYdenbergEcolLet2001.pdf

Protandrous arrival timing to breeding areas: a review

The spruce bark beetle, Ips typographus Linnaeus (Coleoptera: Scolytidae), is the most destructive scolytid in the coniferous forests of the palaearctic region. In Europe, outbreaks may lead to the destruction of millions of Norway spruces [Picea abies (Linnaeus) Karsten], its principal host tree. In Northeastern Asia a subspecies, Ips typographus Linnaeus f. japonicus Niijima, may cause severe damage to spruces in the group P. jezoensis (Siebold and Zuccarini) Carriere sensu lato.

The Spruce Bark Beetle of Eurasia

Bark Beetle?fungus Symbioses

Bark beetles (order Coleoptera: family Scolytidae) comprise a taxonomic group of species that look similar although they differ widely in their ecology and biochemical adaptations to host trees. This diversity of bark beetle biology, in which each species is adapted to only one or a few host-tree species, has probably resulted from natural selection due to the great variety of trees and their biochemicals. It also is likely that each species of tree has coevolved various chemicals to defend against the herbivorous selection pressures of bark beetles and other insects (Erlich and Raven, 1965; Feeny, 1975; Cates, 1981; Berryman et al., 1985). Host-plant chemicals can be attractive, repellent, toxic, or nutritious to bark beetles and have effects on: (1) finding and accepting the host tree (host selection and suitability); (2) feeding stimulation and deterrence; (3) host resistance; (4) pheromone/allomone biosynthesis and communication; and (5) attraction of predators, parasites, and competitors of bark beetles.

/pdf/host-tree-chemistry-affecting-colonization-in-bark-beetles-3lhjnnnnqj.pdf

Host-Tree Chemistry Affecting Colonization in Bark Beetles

Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can be associated with many. In addition, most of these symbioses are multipartite, with the host beetle associated with two or more consistent partners. Mycangia, structures of the beetle integument that function in fungal transport, have evolved numerous times in the Scolytinae. The evolution of such complex, specialized structures indicates a high degree of mutual dependence among the beetles and their fungal partners. Unfortunately, the processes that shaped current day beetle-fungus symbioses remain poorly understood. Phylogeny, the degree and type of dependence on partners, mode of transmission of symbionts (vertical vs. horizontal), effects of the abiotic environment, and interactions among symbionts themselves or with other members of the biotic community, all play important roles in determining the composition, fidelity, and longevity of associations between beetles and their fungal associates. In this review, I provide an overview of these associations and discuss how evolution and ecological processes acted in concert to shape these fascinating, complex symbioses.

Ecological and Evolutionary Determinants of Bark Beetle —Fungus Symbioses

Experiments and observations were made to study the flight behaviour and dispersal of I. typographus at a hibernation size, inside a forest area and between forest areas, respectively in relation to sex, size and fat content. The following results and conclusions are reached.



Ips typographus beetles grown up in standing trees leave the tree to hibernate in the soil. The beetles hibernate in the soil 0–5 m from the tree in which they has grown up. During hibernation the beetles' fat content reduces with about 50% and when the beetles emerge at springtime, they may react directly to pheromones.



In one day Ips typographus beetles can disperse over long distances (up to 750 m), and a homogenous distribution of the beetles over the forest area is reached as long as no pheromone sources exist that aggregate the beetles. The beetles are able to disperse over long distances (> 8 km) outside forest areas.



The flight intensity of the beetles is positively correlated with temperature; at wind speeds over 1 m sec−1 the beetles fly mostly with the wind, at lower wind speeds they tend to fly against the wind after contact with pheromones.



The dispersal and flight behaviour is not affected by the beetle's sex, size or fat content.



The adult beetles that re-emerge from a tree to establish a second brood are at average larger than the beetles that remain in the tree; the males have built up a new fat reserve before they re-emerge.



It is suggested that the dispersal and flight behaviour of the beetles reduces the effectiveness of mass trapping as a control strategy.



It is hypothesized that a decreasing I. typographus population suffer a high mortality caused by predation and parasitism.



Zusammenfassung

Zerstreuung und Flugverhalten des Fichtenborkenkafers Iyps typographus in Beziehung zu Geschlecht, Grose und Fettgehalt



Experimente und Beobachtungen uber das Flugverhalten und die Zerstreuung der Kafer von I. typographus am Uberwinterungsort sowie allgemein innerhalb und auserhalb von Waldern unter Berucksichtigung des Geschlechts, der Grose und des Fettgehalts fuhrten zu folgenden Ergebnissen.



Die I. typographus-Kafer, die sich in stehenden Baumen entwickelten, verlassen diese, um im Boden in 0–5 m Entfernung von ihrem Entwicklungsbaum zu uberwintern. Wahrend der Uberwinterung verringert sich ihr Fettgehalt um etwa 50%. Wenn die Kafer im Fruhjahr den Boden verlassen, konnen sie direkt auf Pheromone reagieren. Innerhalb eines Tages konnen die Kafer von I. typographus sich uber ein groseres Areal (bis zu 750 m) zerstreuen. Solange sie nicht von Pheromonen aggregiert werden, ist ihre Verteilung im Wald homogen. Auserhalb des Waldes sind die Kafer imstande, lange Distanzen (uber 8 km) zu fliegen. Die Flugintensitat war mit der Temperatur positiv korreliert. Bei Windgeschwindigkeiten uber 1 m/s flogen die Kafer meist mit dem Wind; bei geringerer Windstarke zeigten sie die Tendenz, nach Rezeption von Pheromonen gegen den Wind zu fliegen. Die Zerstreuung und das Flugverhalten wurden vom Geschlecht, der Grose und dem Fettgehalt des Kafers nicht beeinflust. Die adulten Kafer, die einen Baum verlassen, um eine 2. Brut anzulegen, waren im Mittel groser als solche, die im Baum verblieben. Die Weibchen hatten einen neuen Fettkorper aufgebaut, bevor sie den Stamm verliesen.



Es ist anzunehmen, das die Zerstreuung und das Flugverhalten der Kafer die Wirksamkeit des Massenfangs als Bekampfungsmasnahme verringert. Es wird die Hypothese aufgestellt, das eine abnehmende I. typographus-Population eine hohe Mortalitat durch rauberische und parasitische Feinde erleidet.

Dispersal and flight behaviour of the spruce bark beetle Ips typographus in relation to sex, size and fat content

A photometrical method to measure the relative fat content of bark beetles and other small invertebrates is presented The method is less labour intensive than extraction of the fat with petroleum ether A relation is found between the weight of the elytra and the beetle's dry weight which permits comparison of beetle's size by comparing the weight of their elytra From the absolute fat content and the elytra weight the relative fat content (mg fat/mg dry weight) can be calculated



The method described has been used to measure the changes in size and fat content of the spruce bark beetle Ips typographus and the effect of attack density on these characteristics Nine logs in netting cages were attacked by I typographus beetles at attack densities ranging from 015 to 259 entrance holes dm−2 bark The emerging offspring beetles were sampled twice a week and their size and relative fat content measured The following conclusions were reached:



1 Twenty seven percent of the offspring had emerged from the logs by the 16th October when emergence nearly stopped because of low temperatures



2 The males emerged on average before the females



3 The size and fat content of the emerging beetles is positively correlated with the time of emergence



4 The size and fat content of the emerging beetles is negatively correlated with attack density



Zusammenfassung

Zur Wirkung der Befallsdichte auf Grose, Fettgehalt und Schlupfen des Fichtenborkenkafers, Ips typographus L



Eine photometrische Methode zur Messung des relativen Fettgehalts von Borkenkafern und anderer kleiner Invertebraten wird beschrieben Die Methode ist weniger arbeitsaufwendig als die Extraktion des Fettes mittels Petrolather Es wurde eine Relation zwischen dem Elytren-Gewicht und dem Trockengewicht der Kafer gefunden, welche einen Vergleich der Kafergrose an Hand eines Vergleichs des Elytren-Gewichts erlaubt Vom absoluten Fettgehalt und Elytren-Gewicht kann dann der relative Fettgehalt abgeleitet werden



Die beschriebene Methode wurde verwendet, um den Wechsel der Grose und des Fettgehalts von Ips typographus sowie die Wirkung der Befallsdichte auf diese zu messen Neun Stammabschnitte in Gazekafigen wurden von Ips typographus in verschiedener Dichte (0,15 bis 2,59 Einbohrlocher/qdm Rinde) befallen Die schlupfenden Jungkafer wurden zweimal wochentlich gesammelt und hinsichtlich Grose und rel Fettgehalt gemessen Die folgenden Ergebnisse wurden dabei gewonnen:



127% der Nachkommen schlupften aus den Abschnitten um den 16 10, als das Schlupfen durch tiefe Temperaturen fast vollig aufhorte



2 Die Mannchen schlupften durchschnittlich vor den Weibchen



3 Grose und Fettgehalt der schlupfenden Kafer waren positiv korreliert mit der Schlupfzeit



4 Grose und Fettgehalt waren negativ korreliert mit der Befallsdichte

The effect of attack density on size, fat content and emergence of the spruce bark beetle Ips typographus L.1

A simulation model is presented which explains the occurrence of protandry (i.e. males emerge on average before females) in the pine looper Bupalus piniarius. The model calculates the fitness of the moths in relation to their date of emergence during the period of emergence. It is investigated how this fitness is affected by: a) the difference between the mean time of emergence of males and females, b) the age of the moths at copulation, c) the mortality rate and longevity of the moths, d) the flight activity of the males, and e) the density of the moths. The input of the model is based on field data and experimental results. The model shows that a) the difference and the mean time of emergence between males and females is maintained by selection of males, such that they on average emerge 2 days before the females, b) 95% of the females mate on the day of emergence, c) the flight activity of the males together with moth density has a significant effect on the difference in time of emergence between the sexes, d) age-dependent copulation success, mortality rate and longevity do not affect the difference in time of emergence between the sexes. From the results it is concluded that mass trapping of males with pheromone traps does not decrease the percentage of females that mate. It is suggested that competitive mate searching has no effect on the occurrence of protandry.

Peter F. Botterweg

Papers

Dispersal and flight behaviour of the spruce bark beetle Ips typographus in relation to sex, size and fat content

The effect of attack density on size, fat content and emergence of the spruce bark beetle Ips typographus L.1

Prorandry in the Pine Looper, Bupalus Piniarius (Lep., Geometridae); an Explanatory Model