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Posts Tagged ‘pinus’

Heritability of serotiny (2): a molecular approach

December 2nd, 2015 No comments

Not long ago we demonstrated that serotiny (i.e., the capacity to accumulate a seed bank in the canopy until the seeds are released by fire) is an heritable trait in pines [1]. This analysis was based on a classical provenance – progeny common garden experiment. However, trait variability under controlled environmental conditions may not fully reflect the variability observed in the field, and thus this estimate of heritability may not reflect how traits respond to natural selection. This is because there is higher environmental variability in the field and also because garden experiments typically include individuals that would not survive in the field (i.e., artificially increases progeny survival) [2]. With the aim of obtaining a more realistic estimate of heritability of serotiny, we have recently estimate it directly in the field for two pine species (P. halepensis, P. pinaster) [3]. Because in the field it is not possible to construct a pedigree, we used the relatedness among individuals estimated from molecular markers (SNPs) for the same individuals from which we had estimated serotiny previously [4]. The variance in serotiny was modelled incorporating the environmental variability (climate and fire regime) using a Bayesian 'animal model'. As expected, field heritability was smaller (around 0.10 for both species) than previous estimates under common garden conditions (0.20). The difference is not surprising because wild P. halepensis and P. pinaster populations extend over heterogeneous landscapes with large environmental variations. Our results highlight the importance of measuring quantitative genetic parameters in natural populations, where environmental heterogeneity is a critical aspect. The heritability of serotiny, although not high, combined with high phenotypic variance within populations, confirms the potential of this fire-related trait for evolutionary change in the wild [2].

Pinus patula
Fig: Serotinous cones of P, halepensis and P. pinaster can be observed in previous posts (P, halepensis, P. pinaster). The photo here shows serotinous cones of Pinus patula from central Mexico (in a foggy rainy day).

References

[1] Hernández-Serrano, A., Verdú, M., Santos-Del-Blanco, L., Climent, J., González-Martínez, S.C. & Pausas, J.G. 2014. Heritability and quantitative genetic divergence of serotiny, a fire-persistence plant trait. Annals of Botany 114: 571-577.  [doi | pdf | suppl. | blog]

[2] Pausas, J.G. 2015. Evolutionary fire ecology: lessons learned from pines. Trends in Plant Science 20: 318-324. [doi | sciencedirect | cell | pdf]

[3] Castellanos, M.C., González-Martínez, S. & Pausas, J.G. 2015. Field heritability of a plant adaptation to fire in heterogeneous landscapes. Molecular Ecology 24: 5633–5642 [doi | pdf | suppl.]

[4] Hernández-Serrano A., Verdú M., González-Martínez S.C., Pausas J.G. 2013. Fire structures pine serotiny at different scales. American Journal of Botany 100: 2349-2356. [doi | amjbot | pdf | supp. | blog]

 

Fire - wind interactions

October 30th, 2015 1 comment

I've just had the opportunity to see some of the consequences of the hurricane Patricia that affected Jalisco, Mexico, last weekend. Here is the effects on a Pinus dauglasiana forest in the Sierra de Manantlán biosfere reserve. Some parts of this forest had burned several years ago (< 10 years) mainly as understory fire, and some trees were injured at the base but most survived (as in any typical undertory fires); there were also some crowning in small patches. Fire killed many understory fire-sensitive broadleaved shrubs, and were replaced by a high density of the pine seedlings (Fig. 1); there were also some plants resprouting (e.g., Quercus, Arbutus, etc.). Now, the strong winds of the hurricane is interacting with fire in two ways: (1) the wind have killed some of the fire-injured trees that had survived the fire (Fig. 1); and (2) the wind has greatly increased the fuel in the forest floor, even in the places where trees were not blown down (Fig. 2), which implies an increase in the chance for a surface fire of high intensity during the next dry season. That is, this seems an opportunity to study the interaction between these two disturbances, fire and hurricanes.

Pinus dauglasianaFig. 1. Pinus dauglasiana forest after a fire (see the seedling regeneration) followed by an hurricane.

Pinus dauglasiana 2Fig. 2. The forest floor of the Pinus dauglasiana forest (unburned) has greatly increased the fuel after the hurricane even in the places where trees were not blown down; the whole forest has a carpet of recently fallen branches and leaves.

Evolutionary fire ecology in pines

April 1st, 2015 No comments

Fire is an ancient and recurrent disturbance factor in our planet and has been present since the origin of terrestrial plants [1]. However, demonstrating whether fire has acted as an evolutionary force is not an easy task [2]. In this context, the emerging discipline of evolutionary fire ecology aims to understand the role of wildfires in shaping biodiversity. In a recent review paper I summarize what we have learned on evolutionary fire ecology by studying the iconic genus Pinus [3]. I suggest that the study of pines has greatly increased our understanding of the role of fire as an evolutionary pressure on plants.

Macro-evolutionary studies of the genus Pinus provide the oldest current evidence of fire as an evolutionary pressure on plants and date back to ca. 125 Million years ago (Ma). Micro-evolutionary studies show that fire traits are variable within and among populations, and especially among populations subject to different fire regimes. In addition, there is increasing evidence of an inherited genetic basis to variability in fire traits. Added together, pines provide compelling evidence that fire can exert an evolutionary pressure on plants and thus shape our biodiversity. In addition, evolutionary fire ecology is providing insights to improve the management of our pine forests under changing conditions. The lessons learned from pines may guide research on the evolutionary ecology in other taxa.

pinus-serotiny
Figure: Example of trait divergence among populations living under different fire regime. Serotiny (as % of closed cones) in populations living under frequent crown fires (red boxes) and in populations where crown-fires are rare (green boxes) for two pine species, Pinus halepensis (Allepo pine, left) and P. pinaster (maritime pine, right).

References
[1] Pausas, J.G. and Keeley, J.E. 2009. A burning story: The role of fire in the history of life. Bioscience 59: 593-601. [doi | jstor | BioOne | pdf]

[2] Keeley, J.E., Pausas, J.G., Rundel, P.W., Bond, W.J. & Bradstock, R.A. 2011. Fire as an evolutionary pressure shaping plant traits. Trends in Plant Science 16: 406-411. [doi | sciencedirect | trends | pdf]

[3] Pausas, J.G. (2015) Evolutionary fire ecology: lessons learned from pines. Trends in Plant Science 20(5): 318-324. [doi | sciencedirect | pdf]

 

Heritability of serotiny

September 29th, 2014 No comments

Evolution by mean of natural selection requires three conditions: there is variation in the trait, this variation is linked to differences in fitness, and the variation is heritable (Darwin!). In many traits we do not have reliable information for the three processes. For a serotinous species, there is evidence that the level of serotiny is variable, and specially it varies in relation to the fire regime of the population. This is because serotiny increases fitness in crown-fire ecosystems and it is not advantageous in ecosystems that do not suffer frequent fires or in ecosystems with understory fires. We recently studied how serotiny of two pine species (Pinus halepensis and Pinus pinaster) varies within population and between populations with different fire regimes and also provided a meta-analysis of the relation between serotiny and fire from other published studies [1]. We also performed a genetic association study for serotiny using SNPs and showed that 17 loci explained ca. 29% of the serotiny variation found in the field in Pinus pinaster [2], suggesting that serotiny variation have a genetic basis. In our most recent paper we provide the first estimate of heritability for a fire trait; specifically we computed the norrow-sense heritability (h2) of serotiny in Pinus halepensis using the common garden approach [3]. We also evaluated whether fire has left a selection signature on the level of serotiny among populations by comparing the genetic divergence of serotiny with the expected divergence of neutral molecular markers (QST – FST comparison). Serotiny showed a significant heritability (h2 = 0.20). The quantitative genetic differentiation among provenances for serotiny (QST= 0.44) was significantly higher than expected under a neutral process (FST = 0.12), suggesting adaptive differentiation. Overall we showed that serotiny is a heritable trait and that it has been shaped by natural selection driven by fire.

ph-serotiny
Figure: Serotinous cones of Pinus halepensis (Foto: J.G. Pausas)

References:

[1] Hernández-Serrano A., Verdú M., González-Martínez S.C., Pausas J.G. 2013. Fire structures pine serotiny at different scales. American Journal of Botany 100 (12): 2349-2356. [doi | amjbot | pdf | supp. | blog]

[2] Budde, K. B., Heuertz, M., Hernández-Serrano, A., Pausas, J.G., Vendramin, G.G., Verdú, M. & González-Martínez, S.C. 2014. In situ genetic association for serotiny, a fire-related trait, in Mediterranean maritime pine (Pinus pinaster Aiton). New Phytologist 201: 230-241.  [doi | pdf | supp1 | supp2]

[3] Hernández-Serrano, A., Verdú, M., Santos-Del-Blanco, L., Climent, J., González-Martínez, S.C. & Pausas, J.G. 2014. Heritability and quantitative genetic divergence of serotiny, a fire-persistence plant trait. Annals of Botany 114: 571-577. [doi | pdf | suppl.]

 

Serotiny

November 16th, 2013 No comments

Serotiny is the delayed seed release for more than a year by retaining the seeds in a woody structure [1]. This implies an accumulation of a canopy seed bank. Serotiny confer fitness benefits in environments with frequent crown-fires, as the heat opens the cones and seeds are dispersed in the post-fire bed which is rich in resource and the competition and predation are low. It is typical of many Proteaceae and some conifers, like some pine species [1, 2; figure below].

Two recent papers analyse the serotiny of two mediterranean pines Pinus halepensis and Pinus pinaster [3, 4]. P. halepensis show higher proportion of serotinous cones than P. pinaster, but the latter retain the cones for longer [3]. The two species show high variability of serotiny within and between populations, but they show a clear pattern of higher serotiny in populations subject to high frequency of crown-fires than those living in areas where crown-fires are rare or absent. This is true either considering serotiny as the proportion of serotinous cones or as the age of the cones stored. Compared with other pines worldwide, the strength of the fire-serotiny relationship in P. pinaster is intermediate, and in P. halepensis is among the highest known [3]. For P. halepensis (the species with higher % serotiny), populations in high fire recurrence regimes have higher fine-scale spatial aggregation of serotiny than those inhabiting low fire recurrence systems. This phenotypic spatial structure generated by fire could be a consequence of the spatial genetic structure of the population. The second study used genomic tools to search for a genetic association for serotiny [4]. The analysis of 384 SNPs of 199 individuals of P. pinaster (in 3 populations included in the previous study [3])  shows that 17 loci were associated with serotiny and explain all together ca. 29% of the serotiny variation found in the field. All these results adds further evidence to the emerging view that fire shapes intraspecific variability of traits and generates phenotypic divergence between populations [5, 6, 7].

Figure: Serotinous cones of Pinus pinaster (Foto: K.B. Budde)

References:

[1] Keeley J.E., Bond W.J., Bradstock R.A., Pausas J.G. & Rundel P.W. 2012. Fire in Mediterranean Ecosystems: Ecology, Evolution and Management. Cambridge University Press.  [The book]

[2] He T, Pausas JG, Belcher CM, Schwilk DW, Lamont BB. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytologist 194: 751-759. [doi | wiley | pdf (suppl.)]

[3] Hernández-Serrano A., Verdú M., González-Martínez S.C., Pausas J.G. 2013. Fire structures pine serotiny at different scales. American Journal of Botany 100: 2349-2356 [doi | amjbot | pdf | supp.]

[4] Budde, K. B., Heuertz, M., Hernández-Serrano, A., Pausas, J.G., Vendramin, G.G., Verdú, M. & González-Martínez, S.C. 2014. In situ genetic association for serotiny, a fire-related trait, in Mediterranean maritime pine (Pinus pinaster Aiton). New Phytologist  201: 230-241 [doi | pdf]

[5] Keeley J.E., Pausas J.G., Rundel P.W., Bond W.J., Bradstock R.A. 2011. Fire as an evolutionary pressure shaping plant traits. Trends in Plant Science 16(8): 406-411. [doi] [trends] [pdf]

[6] Pausas, J. G., Schwilk, D. W. 2012. Fire and plant evolution. New Phytologist, 193:301-303. [doi | wiley | pdf]

[7] Pausas J.G., Alessio G., Moreira B. & Corcobado G. 2012. Fires enhance flammability in Ulex parviflorusNew Phytologist 193: 18-23. [doi | wiley | pdf]

 

Fire and the evolution of pine life histories

August 15th, 2012 No comments

Many pines species are fire adapted. In 1998, JE Keeley & PH Zedler provided a seminal paper showing the various fire adaptations of pines, and the relation between the different adaptations and the different fire regimes [1]. Recent phylogenetic [2,3] and conceptual [4,5] advances in fire ecology have allowed to better understand the evolutionary role of fire in plants, and specifically in pines [2-6]. In a recent paper, JE Keeley provides a new review on the ecology and evolution of pine life histories [7]. Pinus originated ~150 Ma in the mid-Mesozoic Era and radiated across the northern continent of Laurasia during the Cretaceous period, when fire activity was high [3]. Pines have followed two evolutionary strategies interpreted as responses to competition by the newly emerging angiosperms: 1) The Strobus lineage mostly has radiated into stressful sites of low nutrient soils and extremes in cold or heat; ans 2) The Pinus (subgenus) lineage has radiated into fire-prone landscapes with diverse fire regimes. Based on the life history traits associated to fire, JE Keeley define four pine syndromes [7]: fire-avoiders (no fire-adapted; with thin bark), fire-toleraters (adapted to surface fires; with thick bark and self-pruning of dead branches; tall pines), fire-embracers (adapted to crown fires; with retention of dead branches and serotinous cones), and fire-refugia (with marked metapopulation dynamics) strategies.

Figure: Basal fire scar (a) and cross-section of pine with previous fires delineated (b) demonstrating fire survival after recurrent fires. Photos by JE Keeley from [7].

References
[1] Keeley J.E. & Zedler P.H. 1998. Evolution of life histories in Pinus. In: Ecology and biogeography of Pinus (ed. Richardson DM). Cambridge University Press Cambridge (UK), pp. 219-250.

[2] Schwilk D.W. & Ackerly D.D. 2001. Flammability and serotiny as strategies: correlated evolution in pines. Oikos, 94, 326-336. [doi]

[3] He T., Pausas J.G., Belcher C.M., Schwilk D.W. & Lamont B.B. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytol., 194, 751-759. [doi | wiley | pdf ]

[4] Pausas, J. G. and J. E. Keeley. 2009. A burning story: The role of fire in the history of life. Bioscience 59: 593-601. [doi | jstor | pdf]

[5] Keeley, J. E., J. G. Pausas, P. W. Rundel, W. J. Bond, and R. A. Bradstock. 2011. Fire as an evolutionary pressure shaping plant traits. Trends in Plant Sci. 16:406-411.  [doi | pdf]

[6] Pausas J.G. & Schwilk D.W. 2012. Fire and plant evolution. New Phytol., 193, 301-303.  [doi | wiley | pdf]

[7] Keeley J.E. 2012. Ecology and evolution of pine life histories. Ann. For. Sci., 69, 445–453. [doi]

 

The age of fire adaptations

February 20th, 2012 No comments

How old are wildfires? Probably as old as terrestrial ecosystems [1]. The origin of fire is tied to the origin of land plants, which are responsible for two of the three elements essential to the existence of fire: oxygen and fuel. The third element, a heat source, has probably been available throughout the history of the planet (mainly through lightning). There is charcoal evidencs of fires already in the Silurian (440 Ma). However, the existence of fire does not necessarily mean that fire was playing an evolutionary role at that time. So when did fire start to play an evolutionary role generating fire adaptations [2, 3]? By mapping fire adaptation onto a dated phylogeny of Pinaceae, we recently demonstrated [4] that at least, and for this family, fire was an agent of natural selection since about 90-125 Ma! This is far back from what was known until now [4]. At this time, fire-protective thick barks were originated in Pinus species as response to surface fires. With increasing fire intensity, thicker barks and serotiny appeared by 70-90 Ma. These innovations appear at the same time as the Earth’s paleoatmosphere experienced elevated oxygen levels that led to high burn probabilities (mid-Cretaceous). That is, the fiery environments of the Cretaceous strongly influenced trait evolution in Pinus. Whether fire had an evolutionary role prior to this is a challance for future research.

Fotos: In many pines, the thick bark and the discontinuity between the canopy and the understory (self-pruning) allows survival after surface fires (left: Pinus nigra, eastern Spain). Serotinous cones allow a quick seed regeneation after crown fire (right: P. halepensis, eastern Spain). Photos: JG Pausas

References
[1] Pausas, J. G. and J. E. Keeley. 2009. A burning story: The role of fire in the history of life. Bioscience 59: 593-601. [doijstor | BioOne | pdf]

[2] Keeley, J. E., J. G. Pausas, P. W. Rundel, W. J. Bond, and R. A. Bradstock. 2011. Fire as an evolutionary pressure shaping plant traits. Trends in Plant Science 16:406-411. [doi | trends | pdf] | For managers]

[3] Pausas, J. G. and D. W. Schwilk. 2012. Fire and plant evolution. New Phytologist 193:301-303. [doiwileypdf]

[4] He T., Pausas J.G., Belcher C.M., Schwilk D.W., Lamont B.B. (2012). Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytologist 194: 751-759 [doi | wileypdf]

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