498
between particular dietary substrates and clade richness. Moreover, there was no
evidence that clade richness promoted the evolution of antagonisms such as ectoparasitism and parasitoidism. A major conclusion of the study was that taxa with
specialized feeding ecologies such as ectoparasitism and parasitoidism exhibited
significant phylogenetic clustering and thus were closely related to other taxa with
the same diet than to other such taxa with different diets. The results of the study are
consistent with previous evaluations (Wiegmann et al. 1993) that failed to demonstrate a stable relationship between parasitoidism and clade richness. These conclusions also highlight the strong dietary conservatism for parasitoid insect families
that originated during the mid Mesozoic.
The issue of what caused the triggering of the MMPR is a difficult issue to
address. Nevertheless, there are several preconditions that are germane to the issue.
The MMPR required multiple steps of biological organization that produced a cascade of events beginning in the late Early Jurassic that was entrenched by the late
Early Cretaceous. First, an essential prerequisite was the establishment of
Holometabola, which already was present during the Late Carboniferous (Haug
et al. 2015). Second, was the development of several key innovations, particularly:
(1) the specialized drilling ovipositor of apocritan Hymenoptera; (2) the development of the host-seeking triungulin and planidium first-instar stages of Neuroptera,
Coleoptera, Strepsiptera and Diptera; and (3) the telescoped ovipositor of Diptera
(Feener and Brown 1997; Gauld 2008; Evans and Steury 2012). Third, was the ecological restructuring of terrestrial ecosystems such that bottom–up, resource-driven
food-web structure was replaced by top–down regulation with the emergence of the
parasitoid guild that more efficiently regulated primary consumers such as herbivores (Labandeira 2015). Whether the accumulation of these phylogenetic, morphological and ecological aspects caused the separation of the early MMPR into phases
1 and 2, and what propelled phases 3 and 4 during the Late Cretaceous through the
Cenozoic, remains a question for further analyses of more finely resolved data.
A related, albeit vexing, issue involves the evolution of the parasitoid community
and its component guilds (Mills 1994). The particular issue of concern is whether
host evolution of parasitoid lineages proceed from generalist to specialist, the traditional view, or alternatively from specialist to generalist, the uncommon perspective. The traditional version of parasitoid host breadth is that the parasitoid penchant
for high animal host specificity in resources results from high extinction rates and a
low rate of diversification (Stireman III 2005). Such a view would indicate that hostrange evolution proceeds from generalist to specialist and thus should preferentially
occur at the terminal lineages of clades. A test of this hypothesis used tachina flies
(Diptera: Tachinidae) and it was found, surprisingly, that generalist taxa were iteratively derived from specialist taxa (Gauld et al. 1992; Stireman III 2005). This result
highlighted problems in ancestral state reconstruction in previous phylogenetic
trees and the need for additional evidence in establishing parasitoid host specificities. Although it is unclear if the specialist-to-generalist pattern in Tachinidae is
typical of most parasitoid insects (Stireman 2003; Stireman III 2005), other studies,
albeit more limited, have displayed an opposite pattern (Eggleton and Gaston 1992;
C. C. Labandeira and L. Li
between particular dietary substrates and clade richness. Moreover, there was no
evidence that clade richness promoted the evolution of antagonisms such as ectoparasitism and parasitoidism. A major conclusion of the study was that taxa with
specialized feeding ecologies such as ectoparasitism and parasitoidism exhibited
significant phylogenetic clustering and thus were closely related to other taxa with
the same diet than to other such taxa with different diets. The results of the study are
consistent with previous evaluations (Wiegmann et al. 1993) that failed to demonstrate a stable relationship between parasitoidism and clade richness. These conclusions also highlight the strong dietary conservatism for parasitoid insect families
that originated during the mid Mesozoic.
The issue of what caused the triggering of the MMPR is a difficult issue to
address. Nevertheless, there are several preconditions that are germane to the issue.
The MMPR required multiple steps of biological organization that produced a cascade of events beginning in the late Early Jurassic that was entrenched by the late
Early Cretaceous. First, an essential prerequisite was the establishment of
Holometabola, which already was present during the Late Carboniferous (Haug
et al. 2015). Second, was the development of several key innovations, particularly:
(1) the specialized drilling ovipositor of apocritan Hymenoptera; (2) the development of the host-seeking triungulin and planidium first-instar stages of Neuroptera,
Coleoptera, Strepsiptera and Diptera; and (3) the telescoped ovipositor of Diptera
(Feener and Brown 1997; Gauld 2008; Evans and Steury 2012). Third, was the ecological restructuring of terrestrial ecosystems such that bottom–up, resource-driven
food-web structure was replaced by top–down regulation with the emergence of the
parasitoid guild that more efficiently regulated primary consumers such as herbivores (Labandeira 2015). Whether the accumulation of these phylogenetic, morphological and ecological aspects caused the separation of the early MMPR into phases
1 and 2, and what propelled phases 3 and 4 during the Late Cretaceous through the
Cenozoic, remains a question for further analyses of more finely resolved data.
A related, albeit vexing, issue involves the evolution of the parasitoid community
and its component guilds (Mills 1994). The particular issue of concern is whether
host evolution of parasitoid lineages proceed from generalist to specialist, the traditional view, or alternatively from specialist to generalist, the uncommon perspective. The traditional version of parasitoid host breadth is that the parasitoid penchant
for high animal host specificity in resources results from high extinction rates and a
low rate of diversification (Stireman III 2005). Such a view would indicate that hostrange evolution proceeds from generalist to specialist and thus should preferentially
occur at the terminal lineages of clades. A test of this hypothesis used tachina flies
(Diptera: Tachinidae) and it was found, surprisingly, that generalist taxa were iteratively derived from specialist taxa (Gauld et al. 1992; Stireman III 2005). This result
highlighted problems in ancestral state reconstruction in previous phylogenetic
trees and the need for additional evidence in establishing parasitoid host specificities. Although it is unclear if the specialist-to-generalist pattern in Tachinidae is
typical of most parasitoid insects (Stireman 2003; Stireman III 2005), other studies,
albeit more limited, have displayed an opposite pattern (Eggleton and Gaston 1992;
C. C. Labandeira and L. Li