Barbara L. Thorne

Phylogeny of the Dictyoptera

Abstract. Relationships among six key dictyopteran taxa (Mantodea; Blattodea (excluding Cryptocercidae); Cryptocercidae; Mastotermes darwiniensis, Termopsidae and Kalotermitidae [Isoptera]) are analysed based on seventy morphological, developmental and behavioural characters. The fossil record and the ‘living fossil’ genera Cryptocercus, Mastotermes and Archotermopsis are discussed in detail. Exact analysis of the character state matrix by implicit enumeration (Hennig86) resulted in one cladogram, strongly supporting Blattodea + Cryptocercidae as a sister group to Mantodea, with the Isoptera as a sister group to that complex. Arrangements within the termites are equivocal, with Termopsidae and Mastotermes darwiniensis possible as the relatively most primitive element of Isoptera.

Polygyny in the Neotropical termite Nasutitermes corniger: life history consequences of queen mutualism

Summaryecological aspects of monogyny and polygyny in social insect colonies are important in comparing individual queen reproductive success. Inseminated, fecund, multiple foundresses are common in some groups of ants and eusocial wasps, but true polygyny in termites has not previously been studied. One third of Nasutitermes corniger (Isoptera: Termitidae) colonies sampled in areas of young second growth in Panama contained from 2–33 primary queens (not supplementary or neotenic reproductives). All queens in polygynous associations were fully pigmented, physogastric egg layers within a single royal cell. Multiple kings were found less frequently; true polyandry is apparently restricted to immature polygynous colonies.Data on queen weight and morphological features, and on colony composition, show that queens in polygynous nests are young and that a transition from polygyny to monogyny probably occurs after several years. The escalated growth rate of multiple queen colonies removes them from the vulnerable incipient colony size class more rapidly than colonies initiated by a single foundress, and gives them sufficient neuter support staff (workers and soldiers) to enable earlier production of fertile alates. Using a population model (Leslie matrix) I construct isoclines of equal population growth which show values of early age class probability of survival and reproductive output favoring monogyny or polygyny under individual selection. This model of queen mutualism accounts for the risk of a female in a polygynous group not succeeding as the final surviving queen.Multiple primary queens are considered rare in termites, but a review of the literature demonstrates that they may be more widespread than is currently recognized. Polygyny in termites has received scant attention but is of significance as an example of a further ecological and evolutionary convergence between the phylogenetically independent orders Isoptera and Hymenoptera.

Polygyny in termites: Multiple primary queens in colonies ofNasutitermes corniger (Motschuls) (Isoptera: Termitidae)

SummaryThe Neotropical termiteNasutitermes corniger is facultatively polygynous. In areas of young second growth in the Republic of Panamá, polygynous colonies were found commonly. Of 35 nests collected with at least one queen, 12 colonies had from 2–22 primary (first-form) queens. All females were physogastric, fully pigmented, functional egg layers. Polygynous nests had one royal cell, sometimes with multiple chambers. The queens showed no aggression toward one another under laboratory conditions. All queens within an association were of approximately the same size and weight.It appears that polygynous colonies can be formed through budding of a parent nest and queening by several sibs from the parental colony (multiple adultoid reproductives). Formation may also be possible by cooperative co-founding of a nest by sibling queens without workers. Replacement of the original queen by more than one daughter may occur inN. corniger, but it is unlikely to be the sole method of generating polygyny in this species.Polygynous nests may grow faster, have a higher probability of survival, and a lower age of first reproduction than monogynous neighbors. I therefore predict that polygyny will prove most common in habitats where the probability of survival is low and rapid colony growth is advantageous.ZusammenfassungDie Neotropische TermiteNasutitermes corniger ist fakultativ polygyn. In Gebieten jungen Sekundär Waldes der früheren Kanalzone, Panama, wurden häufig polygyne Kolonien gefunden. Von 35 Nestern die zumindest eine Königen enthielten, hatten 12 Kolonien zwischen 2–22 Primär-Königinne. Alle Weibchen dieser vielfachen Vergesellschaftung waren physogastrische, voll pigmentiert und funktionelle Eierlegerinnen. Die polygynen Nester hatten eine Königinnen-Zelle mit manchmal mehreren Kammern. Unter Laborbedingungen verhielten sich die Königinnen nicht aggressiv untereinander. Alle Königinnen in einer Vergesellschaftung hatten ungefähr die gleiche Größe und Gewicht.Es scheint, daß polygyne Kolonien durch Abspaltung des Elternnestes entstehen, und daß die vielfachen Königinnen im neuen Nest Geschwister sind. Möglicherweise können polygyne Kolonien auch durch kooperative Nestgründung zustande kommen. Die ursprüngliche Königin inN. corniger Kolonien, könnte auch durch mehrere Töchter ersetzt werden, doch ist es unwahrscheinlich, daß dies die einzige Methode ist wie es zur Polygynie bei dieser Art kommt.Polygyne Nester wachsen wahrscheinlich schneller, haben eine größere Uberlebenschance und reproduzieren schneller als monogyne Nachbarn. Es wird angenommen, dass Polygynie besonders häufig in den Habitaten vorkommt, in denen die Uberlebenschance gering ist und wo ein schnelles Wachstum der Kolonie von Vorteil ist.

Alate production and sex ratio in colonies of the Neotropical termite Nasutitermes corniger (Isoptera; Termitidae)

Summary1.Dissections of 49 entire Nasutitermes corniger (Motschulsky) colonies collected in Panama immediately prior to the nuptial flights give data on numbers, biomass and sex ratio of alates produced by individual colonies.2)Twenty-six other colonies were collected and dissected in the early period of alate nymph development. Alate nymphs proceed through five instars, spending 5–8 months within the parental colony.3)Even when comparing colonies of similar size, variation in reproductive output among N. corniger colonies in a population is marked. Mature colonies (neuter population size 50,000–400,000) generally produce 5,000–25,000 alates, although some large colonies had no fertile brood, at least during the year they were censused.4)On average, colonies which produce alates have 35% of the colony biomass invested in alates (or late instar nymphs) shortly before the nuptial flight.5)Female N. corniger alates are 1.2–1.4 times heavier (dry weight) than male nestmates. Numerical sex ratio among colonies is skewed toward males, while biomass “investment” sex ratio is not significantly different from 1:1. These data conform to Fishers amended theory of expected sex ratio.

Chemical variation in defensive secretions of four species of Nasutitermes

Abstract Nineteen monoterpenes and 13 diterpenes were distinguished in soldier defensive secretions of four species of Nasutitermes . Samples of N. columbicus, N. corniger, N. ephratae and N. nigriceps were collected in Costa Rica and Panama. Interspecifically, these species can be differentiated by monoterpenes, which exhibit a complex pattern. Intraspecifically, there is detectable variation in monoterpenes and diterpenes, each of which allows discrimination of four populations of N. corniger . Similarity between two Pacific populations of N. corniger from different environments, a tropical dry forest and a rainforest, suggests there is no climatic influence on chemical compositions of defensive secretions. In addition, results from Costa Rica provide evidence that the Atlantic population of N. corniger is derived from Pacific populations.

Ergatoid reproductives in Nasutitermes corniger (Motschulsky) (Isoptera: Termitidae)

Abstract Several hundred ergatoid reproductives were found in a queenless colony of Nasutitermes corniger (Isoptera: Termitidae) in the Republic of Panama. The ergatoids are derived in 2 molts from both small (male) and large (female) workers. The transition series of molting individuals found in this colony demonstrated that: (1) ergatoids are derived from more than one worker instar; (2) sexual transformation is initiated in a worker before molting into an ergatoid; (3) the transition is prolonged enough so that all stages are found concurrently in one colony; and (4) ergatoids are probably fed by normal workers beginning in the instar prior to differentiation. Morphological and histological analyses revealed that ergatoid size, pilosity, fat body, and endocrine glands are enlarged compared with sterile workers. Ocelli and reduced eyes appear in ergatoids, but they are probably not functional. Development of genital organs is conspicuous but the ovaries never reach a complete oogenesis and, in some cases, degenerate. Ergatoid development in the phylogenetically advanced termite genus Nasutitermes appears to be quite rare, but their maturation as replacement reproductives seems a real possibility.

Numerical and biomass caste proportions in colonies of the termitesNasutitermes corniger andN. ephratae (Isoptera; Termitidae)

SummaryCaste ratios among monogynousN. corniger colonies are less variable (higher correlation coefficients and lower variances) than among polygynous colonies. Polygynous colony caste proportions are more constant than for queenless colonies.Correlation coefficients are not significantly different between numerical and biomass neuter caste ratios (large workers: small workers; total worker population: soldiers) inN. corniger orN. ephratae.The intraspecific range of both numerical and biomass percentages of soldiers, small workers, and large workers is large inN. corniger andN. ephratae.Numerical and biomass percentage of soldiers, small workers, and large workers were all significantly different between monogynousN. corniger and monogynousN. ephratae colonies. Mean individual weights of soldiers, large workers, and small workers did not differ between species.Single queenN. corniger colonies tend to have a higher ratio of the number of small workers: large workers and the number of soldiers: workers, and a lower proportion of presoldiers: soldiers than do monogynousN. ephratae nest.PolygynousN. corniger colonies have a statistically larger ratio of number of larvae: number of workers, and a higher number of presoldiers: soldiers than do single queen colonies. These all suggest differences in growth rate related to single versus multiple queens. Monogynous and polygynous nests have significantly higher ratios of larvae: workers than do queenless colonies.In both numerical and biomass analyses of variousN. corniger caste ratios, correlation coefficients were highest in comparisons between the total number or dry weight of all workers vs soldiers.Mean individual dry weights of large and small workers in queenlessN. corniger colonies are significantly higher than in queenright colonies. This may be because the queenless colony population is aging without generating more young so fewer individuals are in the early worker instars.ZusammenfassungDie numerischen Proportionen der Kasten sind bei monogynenN.c. Kolonien weniger variabel (höherer Korrelationskoeffizient und niedrigere Abweichung) als bei polygynen Kolonien. Polygyne Kolonien sind konstanter in ihren Kasten-Proportionen als Kolonien ohne Königinnen.Die Korrelationskoeffizienten von Mengen- und Gewichtsverhältnissen unter den sterilen Kasten (grosse Arbeiter: kleine Arbeiter; gesamte Arbeiter Population: Soldaten) sind weder beiN.c. noch beiN.e. signifikant verschieden.Sowohl beiN.c. wie auch beiN.e. findet man eine weite innerartliche Verteilung von proportionalen Anteilen von Soldaten, kleinen Arbeitern, und grossen Arbeitern.Der zahlen- und gewichtsmässige Anteil der Soldaten, kleinen und grossen Arbeitern, war zwischen monogynenN.c. Kolonien und monogynenN.e. Kolonien signifikant unterschiedlich. Das mittlere Gewicht von Soldaten, grossen Arbeitern und kleinen Arbeitern war nicht unterschiedlich zwischen den beiden Arten.In monogynenN.c. Kolonien ist gewöhnlich das Zahlenverhältnis zwischen kleinen Arbeitern: grossen Arbeitern, und Soldaten: Arbeitern grösser, dagegen ist das Verhältnis zwischen Prä-Soldaten: Soldaten kleiner als bei monogynenN.e. Kolonien.PolygyneN.c. Kolonien haben ein statistisch grösseres Zahlenverhältnis von Larven: Arbeitern, und Prä-Soldaten: Soldaten, als monogyne Kolonien. Dies alles lässt vermuten, dass monogyne und polygyne Kolonien unterschiedliche Wachstumsraten haben.Bei der Analyse der Zahlen- und Gewichtsverhältnisse verschiedenerN.c. Kasten waren die Korrelationskoeffizienten am höchsten beim Vergleich von Gesamtzahl oder Trockengewicht der Arbeiter versus Gesamtzahl oder Trockengewicht von Soldaten.Das durchschnittliche Trocken gewicht grosser und kleiner Arbeiter in königinlosen Kolonien war signifikant höher als in Kolonien mit Königin. Dies ist wahrscheinlich deshalb so, weil die Population der königinlosen Kolonie älter wird, ohne mehr Jungtiere zu produziern, sodass weniger Anfangsstadien von Arbeitern zu finden sind.

Surface hydrocarbon components of two species ofNasutitermes from Trinidad

Colonies ofNasutitermes costalis (Holmgren) andN. ephratae (Holmgren) were collected from five locations in Trinidad. Cuticular hydrocarbons were characterized by gas chromatography-electron impact mass spectrometry and quantified by capillary gas chromatography. Sixteen major components were identified; all but one component (12, 16-dimethyltriacontane) were common to both species. The methyl-branched hydrocarbons were predominant inN. costalis, while the majority of the hydrocarbon components inN. ephratae weren-alkanes. One hydrocarbon (11,15-dimethylheptacosane) was found in abundance in samples ofN. ephratae from Trinidad but was not previously reported from collections of this species in Panama. In addition to the morphology of the soldiers and alates and the architecture of the arboreal nests,N. costalis andN. ephratae from Trinidad can easily be separated by chromatograms of the hydrocarbons.N. costalis has an enormous 13,17-dimethylhentriacontane peak (mean = 42.4% of total hydrocarbon). InN. ephratae this peak is much smaller and the 12,16-dimethyltriacontane peak is completely missing.N. costalis from Trinidad andN. corniger from Panama appear to have cuticular hydrocarbon profiles that are more similar to one another than are those ofN. ephratae from Trinidad and Panama.

Ancestral transfer of symbionts between cockroaches and termites: an alternative hypothesis.

Closely related cellulolytic protozoa reside in the hindguts of extant woodroaches (Cryptocercidae) and termites (Isoptera). The evolutionary origin of these symbiotic relationships in the two lineages is uncertain. Transfer of protozoa between ancestors of modern Cryptocercus and termites remains a valid alternative theory to the established hypothesis of symbiont inheritance from a common ancestor. Nalepa’s (Proc. R. Soc. Lond. B 246, 185 (1991)) concerns regarding the protozoan transfer hypothesis focus on the biology of m odern species, and neglect to consider the evolutionary framework of an ancestral dynamic postulated to occur among Palaeozoic insects. Legitimacy of the symbiont transfer theory removes the constraint of interpreting presence of cellulolytic protozoa as a synapom orphy between Cryptocercidae and Isoptera, with potential im pact on objective resolution of dictyopteran phylogeny.

Ergatoid reproductives in Nasutitermes columbicus (Isoptera, Termitidae)

Numerous functional ergatoid replacement reproductives were found in one colony of Nasutitermes columbicus in Panama. Their morphology was mainly workerlike, although several imaginal characters such as the compound eyes and variable wing buds were more or less developed. The sex organs were fully mature and the fat body of the females, not of the males, was of the “royal” type. The development of the eyes was not accompanied by the differentiation of the optic lobes of the brain, nor was the presence of wing buds correlated with a development of the wing muscles.